Light Emitting Device and Electronic Device

ABSTRACT

An object is to provide a highly reliable light emitting device which is thin and is not damaged by external local pressure. Further, another object is to manufacture a light emitting device with a high yield by preventing defects of a shape and characteristics due to external stress in a manufacture process. A light emitting element is sealed between a first structure body in which a fibrous body is impregnated with an organic resin and a second structure body in which a fibrous body is impregnated with an organic resin, whereby a highly reliable light emitting device which is thin and has intensity can be provided. Further, a light emitting device can be manufactured with a high yield by preventing defects of a shape and characteristics in a manufacture process.

TECHNICAL FIELD

The present invention relates to a light emitting device having lightemitting elements that employ electroluminescence. In addition, thepresent invention relates to an electronic device on which the lightemitting device is mounted as a component.

BACKGROUND ART

In recent years, thin and flat display devices have been needed asdisplay devices in a television, a cellular phone, a digital camera, andthe like, and as the display devices satisfying this need, displaydevices using self-light emitting elements have attracted attention. Oneof the self-light emitting elements is a light emitting elementutilizing electroluminescence (EL), and this light emitting elementincludes a light emitting material interposed between a pair ofelectrodes and can provide light emission from the light emittingmaterial by voltage application.

Compared to a liquid crystal display, such a self-light emitting elementhas advantages such as the fact that its pixels have high visibility andthe fact that it does not need a backlight. Such a self-light emittingelement is considered to be suitable for application as a flat paneldisplay element. In addition, such a self-light emitting element has afeature that the thickness can be reduced and that response speed isextremely fast.

In Reference 1, a flexible electroluminescence light emitting deviceusing techniques of separation and transfer is proposed.

REFERENCE

Reference 1: Japanese Published Patent Application No. 2003-204049

DISCLOSURE OF INVENTION

As the market of the light emitting devices spreads, it is important tomake devices into a thinner shape in miniaturizing products, and thethinning technique and the application range of the miniaturizedproducts spread rapidly. However, when a light emitting device isthinned, a light emitting device, which is formed such that a layerincluding a semiconductor element is transferred to a plastic film orthe like, is cracked by external local pressure, resulting inmalfunctions.

Thus, an object of one embodiment of the present invention is to providea highly reliable light emitting device which is thin and is not damagedby external local pressure. Further, another object is to manufacture alight emitting device with a high yield by preventing a defect in shapeand characteristic due to external stress in a manufacturing process.

A light emitting device according to one embodiment of the presentinvention includes a first structure body in which a fibrous body isimpregnated with an organic resin and a second structure body in which afibrous body is impregnated with an organic resin; and a light emittingelement provided between the first structure body and the secondstructure body. The first structure body and the second structure bodyare in contact with each other and fixed to each other in an end portionto seal the light emitting element.

A light emitting device of one embodiment of the present inventionincludes a first structure body in which a fibrous body is impregnatedwith an organic resin and a second structure body in which a fibrousbody is impregnated with an organic resin; a light emitting elementprovided between the first structure body and the second structure body;and impact relief layers provided on a surface of the first structurebody on which the light emitting element is not provided and on asurface of the second structure body on which the light emitting elementis not provided. The first structure body and the second structure bodyare in contact with each other and fixed to each other in an end portionto seal the light emitting element.

In the light emitting device of one embodiment of the present inventiondescribed above, an insulating layer may be provided between the lightemitting element and the first structure body or the second structurebody.

In the light emitting device of one embodiment of the present invention,a conductive layer may be provided on an outermost surface of the firststructure body or the second structure body on which the light emittingelement is not provided.

Note that in this specification, a light emitting element includes, inits scope, an element whose luminance is controlled by current orvoltage, and specifically includes an inorganic electroluminescent (EL)element, an organic EL element, and the like.

The light emitting device of one embodiment of the present invention maybe either a passive matrix light emitting device or an active matrixlight emitting device. In the passive matrix light emitting device, aplurality of light emitting elements is connected to the sametransistor. Meanwhile, in the active matrix light emitting device, lightemitting elements are each connected to one of transistors.

In this specification, the thickness of the first structure body or thesecond structure body is defined by distance from the outermost surfaceof an element portion sandwiched between the first structure body andthe second structure body, to the surface of the first structure body orthe second structure body.

Note that the terms of degrees which are used in this specification, forexample, “same” or “substantially the same” mean a reasonable amount ofdeviation from the modified term such that the end result is notsignificantly changed. These terms should be construed as including adeviation of at least ±5% of the modified term if this deviation wouldnot negate the meaning of the word it modifies. Note that the ordinalnumbers such as “first” and “second” in this specification are used forconvenience and do not denote the order of steps and the stacking orderof layers. In addition, the ordinal numbers in this specification do notdenote particular names which specify the invention.

A light emitting element is sealed between the first structure body inwhich a fibrous body is impregnated with an organic resin and the secondstructure body in which a fibrous body is impregnated with an organicresin, whereby a highly reliable light emitting device which is thin andhigh-strength can be provided. Further, a light emitting device can bemanufactured with a high yield by preventing defects of a shape andcharacteristics in a manufacture process.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A and 1B illustrate a light emitting device according to anembodiment of the present invention.

FIGS. 2A to 2E illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 3A to 3C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 4A to 4C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 5A to 5D illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 6A to 6C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 7A to 7C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 8A to 8E illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 9A to 9C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 10A to 10C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 11A to 11C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 12A to 12C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 13A to 13C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 14A and 14B each illustrate a light emitting device according toan embodiment of the present invention.

FIGS. 15A to 15D each illustrate a light emitting device according to anembodiment of the present invention.

FIGS. 16A-1, 16A-2, 16B-1, and 16B-2 illustrate a method formanufacturing a light emitting device according to an embodiment of thepresent invention.

FIGS. 17A to 17C illustrate a method for manufacturing a light emittingdevice according to an embodiment of the present invention.

FIGS. 18A and 18B illustrate a light emitting device according to anembodiment of the present invention.

FIG. 19 illustrates an application example of a light emitting deviceaccording to an embodiment of the present invention.

FIGS. 20A and 20B each illustrate an application example of a lightemitting device according to an embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

Embodiments of the present invention will be described in detail withreference to the accompanying drawings. Note that the present inventionis not limited to the following description because it will be easilyunderstood by those skilled in the art that various changes andmodifications can be made without departing from the spirit and scope ofthe present invention. Therefore, the present invention should not beinterpreted as being limited to what is described in the embodimentsdescribed below. In a structure to be given below, the same portions orportions having similar functions are denoted by the same referencenumerals in different drawings, and description thereof will be omitted.

(Embodiment 1)

In this embodiment, an example of a light emitting device which is oneembodiment of the present invention will be described in detail withreference to FIGS. 1A and 1B.

A display portion of a light emitting device of this embodiment isillustrated in FIGS. 1A and 1B. The light emitting device of thisembodiment illustrated in FIG. 1A has an element portion 170 sealedbetween a first structure body 132 and a second structure body 133. Inaddition, an insulating layer 104 and an insulating layer 138 are fowledbetween the element portion 170 and the second structure body 133 andbetween the element portion 170 and the first structure body 132. Thefirst structure body 132 and the second structure body 133 are each astructure body in which a fibrous body 132 a is impregnated with anorganic resin 132 b. In addition, the first structure body 132 and thesecond structure body 133 are in contact with each other and fixed toeach other in a region where the element portion 170 is not provided(e.g., end portions of the first structure body 132 and the secondstructure body 133).

It is preferable for the first structure body 132 and the secondstructure body 133 to use a material in which the modulus of elasticitybe higher than or equal to 13 GPa and the modulus of rupture be lowerthan 300 MPa. In addition, it is preferable for the first structure body132 and the second structure body 133 to have a thickness of greaterthan or equal to 5 μm and less than or equal to 50 μm. Further, it ispreferable that the first structure body 132 and the second structurebody 133 have the same film thickness. When the first structure body 132and the second structure body 133 have the same thickness, the elementportion 170 can be placed in the central portion of the light emittingdevice.

In the first structure body 132 and the second structure body 133, thefibrous body 132 a is woven using warp yarns spaced at regular intervalsand weft yarns spaced at regular intervals. Such a fibrous body which iswoven using the warp yarns and the weft yarns has regions without thewarp yarns and the weft yarns. In the fibrous body 132 a, the fibrousbody 132 a is more easily impregnated with the organic resin 132 b,whereby adhesion between the fibrous body 132 a and a light emittingelement can be increased.

Further, in the fibrous body 132 a, density of the warp yarns and theweft yarns may be high and a proportion of the regions without the warpyarns and the weft yarns may be low.

Further, in order to enhance permeability of an organic resin into theinside of the yarn bundle of fibers, the fiber may be subjected tosurface treatment. For example, as the surface treatment, coronadischarge, plasma discharge, and the like for activating a surface ofthe fiber can be given. Further, surface treatment using a silanecoupling agent or a titanate coupling agent can be given.

Note that a structure body in which a fibrous body is impregnated withan organic resin may have a stacked structure. In that case, thestructure body may be a stack of a plurality of structure bodies in eachof which a single-layer fibrous body is impregnated with an organicresin or may be a structure body in which a plurality of fibrous bodiesstacked is impregnated with an organic resin. In stacking a plurality ofstructure bodies in each of which a single-layer fibrous body isimpregnated with an organic resin, another layer may be interposedbetween the structure bodies.

The element portion 170 sealed between the first structure body 132 andthe second structure body 133 includes at least a light emitting element140 and a switching element for applying potential to the light emittingelement 140. For example, a transistor (e.g., a bipolar transistor or aMOS transistor), a diode (e.g., a PN diode, a PIN diode, a Schottkydiode, a metal-insulator-metal (MIM) diode, ametal-insulator-semiconductor (MIS) diode, or a diode-connectedtransistor), a thyristor, or the like can be used as the switchingelement. Alternatively, a logic circuit in which such elements arecombined can be used as the switching element. In this embodiment, athin film transistor 106 is used as the switching element. In addition,a driver circuit portion may be included in the element portion 170using a light emitting device as a driver integrated type. Note that adriver circuit can be formed outside the element portion which issealed.

The light emitting element 140 is formed such that a first electrode122, an EL layer 134, and a second electrode 136 are stacked. One of thefirst electrode 122 and the second electrode 136 is used as an anode,and the other is used as a cathode.

The EL layer 134 included in the light emitting element includes atleast a light emitting layer. In addition, the EL layer 134 can have astacked structure including a hole injecting layer, a hole transportinglayer, an electron transporting layer, an electron injecting layer,and/or the like, in addition to the light emitting layer. The EL layer134 can be formed using either a low molecular material or a highmolecular material. Note that the material forming the EL layer 134 isnot limited to a material containing only an organic compound material,and may partially contain an inorganic compound material.

Note that materials exhibiting red (R), green (G), and blue (B) may beused when the light emitting device performs full color display toselectively form the EL layer 134. When performing monochrome display, amaterial exhibiting at least one color may be used to fain the EL layer134. In addition, an EL layer and a color filter may be combined. Evenin the case where a single color light emitting layer (for example, awhite light emitting layer) is used, full-color display is possible bythe color filter. For example, when an EL layer using a material fromwhich white (W) light emission is obtained and a color filter arecombined, full color display may be performed with four subpixels, thatis, a pixel without a color filter and RGB pixels.

In the light emitting device illustrated in FIG. 1A, the element portion170 is placed in a substantially central portion of a cross section ofthe light emitting device. In a region where the element portion 170 isnot provided (e.g., end portions of the first structure body 132 and thesecond structure body 133), the first structure body 132 and the secondstructure body 133 are in contact with each other, so that the elementportion 170 is sealed. The fibrous body 132 a of the first structurebody and the second structure body is formed from high-strength fiber,which has a high elongation modulus or a high Young's modulus.Accordingly, even when the local pressure such as point pressure orlinear pressure is applied to the light emitting device, thehigh-strength fiber is not stretched. Pressing force is dispersedthroughout the fibrous body 132 a, and the whole light emitting deviceis curved. That is, a pair of structure bodies sandwiching the lightemitting element functions as impact resistant layers against forceapplied to the light emitting device from the outside. As a result, evenif local pressure is applied, the curve to be generated in the lightemitting device has a large radius of curvature, whereby a lightemitting element sealed between a pair of structure bodies, a wiring,and the like are not cracked and damage of the light emitting device canbe reduced.

Further, when the element portion 170 is formed to have a smallthickness, the light emitting device can be curved. Therefore, the lightemitting device of this embodiment can be bonded to various basematerials. When the light emitting device of this embodiment is attachedto a base material having a curved surface, a display and a lightingdevice each having a curved surface can be realized. In addition, whenthe element portion 170 is thin, a light emitting device can be reducedin weight.

Another structure of a light emitting device of this embodiment which isdifferent from the structure illustrated in FIG. 1A is illustrated inFIG. 1B. A light emitting device of this embodiment illustrated in FIG.1B has a structure in which a first impact relief layer 103 and a secondimpact relief layer 113 are provided on the outer sides of the firststructure body and the second structure body, respectively of the lightemitting device of this embodiment illustrated in FIG. 1A (on sidesopposing the light emitting element 140).

An impact relief layer has an effect of diffusing and reducing force tobe applied to the light emitting device from the outside. Accordingly,as illustrated in FIG. 1B, by providing a structure body functioning asan impact resistant layer against force applied to the light emittingdevice from the outside (also referred to as external stress) and animpact relief layer that diffuses the force, locally applied force tothe light emitting device can be further alleviated. Therefore, thestrength of the light emitting device can be increased, and damage,defective characteristics, and the like of the light emitting device canbe prevented.

It is preferable that the first impact relief layer 103 and the secondimpact relief layer 113 have a lower modulus of elasticity than thefirst structure body 132 and the second structure body 133 and have highbreaking strength. For example, for the first impact relief layer 103and the second impact relief layer 113, a film having rubber elasticityin which the modulus of elasticity is higher than or equal to 5 GPa andless than or equal to 12 GPa and the modulus of rupture is higher thanor equal to 300 MPa can be used.

It is preferable that the first impact relief layer 103 and the secondimpact relief layer 113 be formed using a high-strength material. Astypical examples of a high-strength material, a polyvinyl alcohol resin,a polyester resin, a polyamide resin, a polyethylene resin, an aramidresin, a polyparaphenylene benzobisoxazole resin, a glass resin, and thelike can be given. By providing the first impact relief layer 103 andthe second impact relief layer 113 formed using a high-strength materialwith elasticity, a load such as local pressure is diffused to andabsorbed by the entire layer, so that the light emitting device can beprevented from being damaged.

In more specific, for the first impact relief layer 103 and the secondimpact relief layer 113, an aramid resin, a polyethylene naphthalate(PEN) resin, a polyethersulfone (PES) resin, a polyphenylene sulfide(PPS) resin, a polyimide resin (PI), a polyethylene terephthalate (PET)resin, or the like may be used. In this embodiment, an aramid film withthe use of an aramid resin is used for the first impact relief layer 103and the second impact relief layer 113.

A prepreg that is a structure body in which a fibrous body isimpregnated with an organic resin is used for each of the firststructure body 132 and the second structure body 133; therefore, bondingbetween the first structure body 132 and the first impact relief layer103, bonding between the second structure body 133 and the second impactrelief layer 113, and bonding between the first structure body 132 andthe second structure body 133 can be performed by direct-heating andpressure treatment without a bonding layer interposed therebetween.

Note that as illustrated in FIG. 1B, when a pair of structure bodies anda pair of impact relief layers are symmetrically provided with respectto the element portion 170, force applied to the light emitting devicecan be distributed uniformly; therefore, damage of the element portion170 due to bending, warpage, or the like can be prevented. Further, whena pair of structure bodies is formed using the same material to have thesame thickness and a pair of impact relief layers is formed using thesame material to have the same thickness, an equivalent characteristiccan be provided, whereby the force becomes better distributed. Further,if the total thickness of the first structure body 132 and the firstimpact relief layer 103, or the total thickness of the second structurebody 133 and the second impact relief layer 113 is larger than the totalthickness of the element portion 170, the first structure body 132, thefirst impact relief layer 103, the second structure body 133, and thesecond impact relief layer 113 relieve stress due to bending; therefore,the element portion 170 is less likely to be damaged, which ispreferable.

(Embodiment 2)

In this embodiment, an example of a method for manufacturing a lightemitting device illustrated in FIG. 1A will be described in detail withreference to FIGS. 2A to 2E, FIGS. 3A to 3C, and FIGS. 4A to 4C.

First, a separation layer 102 is formed on a surface of a substrate 100;successively, the insulating layer 104 is famed (see FIG. 2A). Theseparation layer 102 and the insulating layer 104 can be formed insuccession. By forming successively, they are not exposed to the air sothat impurities can be prevented from being contained therein.

For the substrate 100, a glass substrate, a quartz substrate, a metalsubstrate, a stainless steel substrate, or the like may be used. Forexample, when a rectangular glass substrate with a side of one meter ormore is used, productivity can be drastically improved.

Note that in this process, the case where the separation layer 102 isprovided on the entire surface of the substrate 100 is described;however, the separation layer 102 may be provided on the entire surfaceof the substrate 100, and then the separation layer 102 may beselectively removed, so that the separation layer may be provided onlyin a desired region, if needed. In addition, although the separationlayer 102 is formed to be in contact with the substrate 100, aninsulating layer such as a silicon oxide film, a silicon oxynitridefilm, a silicon nitride film, or a silicon nitride oxide film may beformed to be in contact with the substrate 100, if needed, and then theseparation layer 102 may be formed to be in contact with the insulatinglayer.

The separation layer 102 is formed having a single-layer structure or astacked structure of a layer with a thickness of 30 nm to 200 nm, whichis fowled using an element selected from tungsten (W), molybdenum (Mo),titanium (Ti), tantalum (Ta), niobium (Nb), nickel (Ni), cobalt (Co),zirconium (Zr), zinc (Zn), ruthenium (Ru), rhodium (Rh), palladium (Pd),osmium (Os), iridium (Ir), or silicon (Si); or an alloy material or acompound material containing any of the above elements as its maincomponent by a sputtering method, a plasma CVD method, a coating method,a printing method, or the like. The crystalline structure of a layercontaining silicon may be any one of an amorphous state, amicrocrystalline state, or a polycrystalline state. Here, a coatingmethod is a method by which a film is formed by discharging a solutionon an object to be processed and includes a spin coating method and adroplet discharging method. A droplet discharging method is a method forforming a predetermined pattern by discharging a droplet of acomposition containing particulates from a small hole.

If the separation layer 102 has a single-layer structure, the separationlayer 102 is preferably formed using a layer containing tungsten,molybdenum, or a mixture of tungsten and molybdenum. Alternatively, theseparation layer 102 is formed using a layer containing oxide oftungsten, a layer containing oxynitride of tungsten, or a layercontaining oxide or oxynitride of a mixture of tungsten and molybdenum.Note that the mixture of tungsten and molybdenum corresponds to an alloyof tungsten and molybdenum, for example.

When the separation layer 102 has a stacked structure, preferably, ametal layer is formed as a first layer, and a metal oxide layer isformed as a second layer. For example, as the first-metal layer, a layercontaining tungsten or a layer containing a mixture of tungsten andmolybdenum is formed. As the second layer, a layer containing oxide oftungsten, a layer containing oxide of a mixture of tungsten andmolybdenum, a layer containing nitride of tungsten, a layer containingnitride of a mixture of tungsten and molybdenum, a layer containingoxynitride of tungsten, a layer containing oxynitride of a mixture oftungsten and molybdenum, a layer containing nitride oxide of tungsten, alayer containing nitride oxide of a mixture of tungsten and molybdenumis formed.

When the separation layer 102 has a stacked structure in which a metallayer is formed as the first layer and a metal oxide layer is formed asthe second layer, the stacked structure may be formed by utilizing thefollowing: a layer containing tungsten is formed as the metal layer, andan insulating layer made of oxide is formed thereover, whereby a layercontaining oxide of tungsten is formed as the metal oxide layer at theinterface between the layer containing tungsten and the insulatinglayer. Moreover, the metal oxide layer may be formed in such a mannerthat the surface of the metal layer is subjected to thermal oxidationtreatment, oxygen plasma treatment, treatment using a solution havingstrong oxidizability such as ozone water, or the like.

The insulating layer 104 serves as a protective layer and is provided tofacilitate separation at the interface between the separation layer 102and the insulating layer 104 in a subsequent separation step or toprevent a semiconductor element and a wiring from being cracked ordamaged in a subsequent separation step. For example, the insulatinglayer 104 is formed using an inorganic compound to be a single layer ora multilayer by a sputtering method, a plasma CVD method, a coatingmethod, a printing method, or the like. As a typical example of aninorganic compound, silicon oxide, silicon nitride, silicon oxynitride,silicon nitride oxide, and the like can be given.

When silicon nitride, silicon nitride oxide, silicon oxynitride, or thelike is used for the insulating layer 104, entry of moisture or gas suchas oxygen from outside into the element layer to be formed later can beprevented. The thickness of the insulating layer functioning as aprotective layer is preferably greater than or equal to 10 nm and lessthan or equal to 1000 nm, more preferably, greater than or equal to 100nm and less than or equal to 700 nm.

Next, the thin film transistor 106 is formed over the insulating layer104 (see FIG. 2B). The thin film transistor 106 is formed using at leasta semiconductor layer 108 having a source region, a drain region, and achannel formation region; a gate insulating layer 110; and a gateelectrode 112.

The semiconductor layer 108 is a layer formed using a non-single-crystalsemiconductor which has a thickness of greater than or equal to 10 nmand less than or equal to 100 nm, more preferably, greater than or equalto 20 nm and less than or equal to 70 nm. As a non-single-crystalsemiconductor layer, a crystalline semiconductor layer, an amorphoussemiconductor layer, a microcrystal semiconductor layer, and the likecan be given. As the semiconductor, silicon, germanium, a silicongermanium compound, and the like can be given. In particular, it ispreferable to apply a crystalline semiconductor which is formed bycrystallization through laser irradiation, rapid thermal annealing(RTA), heat treatment using an annealing furnace, or a method in whichany of these methods are combined. In the heat treatment, acrystallization method using a metal element such as nickel which canpromote crystallization of silicon semiconductor can be used.

The gate insulating layer 110 is formed from an inorganic insulator suchas silicon oxide and silicon oxynitride with a thickness of greater thanor equal to 5 nm and less than or equal to 200 nm, preferably, greaterthan or equal to 10 nm and less than or equal to 100 nm.

The gate electrode 112 can be formed from a polycrystallinesemiconductor to which metal or an impurity of one conductivity type isadded. When using a metal, tungsten (W), molybdenum (Mo), titanium (Ti),tantalum (Ta), aluminum (Al) or the like can be used. Moreover, metalnitride obtained by nitriding metal can be used. Alternatively, astructure in which a first layer containing the metal nitride and asecond layer containing the metal are stacked may be employed. Byforming the first layer with metal nitride, the first layer can serve asmetal barrier. In other words, the metal of the second layer can beprevented from diffusing into the gate insulating layer or into thesemiconductor layer that is provided in the lower part of the gateinsulating layer. In the case of employing a stacked structure, the gateelectrode may have a shape in which the end portion of the first layerextends beyond the end portion of the second layer.

The thin film transistor 106 which is formed by combination of thesemiconductor layer 108, the gate insulating layer 110, the gateelectrode 112, and the like can employ various kinds of structures suchas a single drain structure, an LDD (lightly doped drain) structure, anda gate overlap drain structure. Here, a thin film transistor having anLDD structure in which a low concentration impurity region is providedusing an insulating layer (also referred to as a “sidewall”) that is incontact with a side surface of the gate electrode 112 is illustrated.Moreover, a multi-gate structure where transistors, to which gatevoltage having the same potential is equally applied, are seriallyconnected; a dual-gate structure where the semiconductor layer issandwiched by gate electrodes; or the like can be used.

As the thin film transistor, a thin film transistor using metal oxide oran organic semiconductor material for a semiconductor layer can be used.As typical examples of the metal oxide, zinc oxide, indium gallium zincoxide, and the like can be given.

Next, a wiring 118 that is electrically connected to a source region anda drain region of the thin film transistor 106 is formed, and the firstelectrode 122 that is electrically connected to the wiring 118 is formed(see FIG. 2C).

Here, insulating layers 114 and 116 are formed to cover the thin filmtransistor 106, and the wiring 118 which can function as a sourceelectrode and a drain electrode is formed over the insulating layer 116.Then, an insulating layer 120 is formed over the wiring 118, and thefirst electrode 122 is formed over the insulating layer 120.

The insulating layers 114 and 116 each serve as an interlayer insulatinglayer. The insulating layers 114 and 116 are formed to have a singlelayer or a stack of an inorganic material such as oxide of silicon ornitride of silicon; an organic material such as polyimide, polyamide,benzocyclobutene, acrylic, or epoxy; a siloxane material; or the like bya CVD method, a sputtering method, an SOG method, a droplet dischargingmethod, a screen printing method, or the like. For example, a siliconnitride oxide film may be formed as the first insulating layer 114, anda silicon oxynitride film may be formed as the second insulating layer116.

The wiring 118 is preferably formed of a combination of a low resistancematerial such as aluminum (Al) and a barrier metal using a high meltingpoint metal material such as titanium (Ti) and molybdenum (Mo), forexample, a stacked structure of titanium (Ti) and aluminum (Al) and astacked structure of molybdenum (Mo) and aluminum (Al).

The insulating layer 120 is formed to have a single layer or a stackusing an inorganic material such as oxide of silicon or nitride ofsilicon, an organic material such as polyimide, polyamide,benzocyclobutene, acrylic, or epoxy, a siloxane material, or the like bya CVD method, a sputtering method, a SOG method, a droplet dischargingmethod, a screen printing method, or the like. Here, the insulatinglayer 120 is formed using epoxy by a screen printing method.

Note that the first electrode 122 is an electrode used as an anode orcathode of a light emitting element. In the case of being used as theanode, a material with a high work function is preferably used. Forexample, a single-layer film such as an indium tin oxide film, an indiumtin oxide film containing silicon, a light-transmitting conductive filmformed by a sputtering method using a target in which indium oxide ismixed with zinc oxide (ZnO) of 2 wt % to 20 wt %, a zinc oxide (ZnO)film, a titanium nitride film, a chromium film, a tungsten film, a Znfilm, or a Pt film; a stack of a titanium nitride film and a filmcontaining aluminum as its main component; a three-layer structure of atitanium nitride film, a film containing aluminum as its main component,and another titanium nitride film; or the like.

A material having a low work function (Al, Ag, Li, Ca, or an alloythereof such as MgAg, MgIn, AlLi, CaF₂, or calcium nitride) ispreferably used for a cathode. In the case where an electrode used as acathode is made to transmit light, a stack of a metal thin film with asmall thickness and a light-transmitting conductive film (an indium tinoxide film, an indium tin oxide film containing silicon, alight-transmitting conductive film formed by a sputtering method using atarget in which indium oxide is mixed with zinc oxide (ZnO) of 2 wt % to20 wt %, a zinc oxide (ZnO) film, or the like) is preferably used as theelectrode.

Next, an insulating layer 123 is fowled to cover end portions of thefirst electrode 122. In this embodiment, the insulating layer 123 isformed using a positive photosensitive acrylic resin film. Theinsulating layer 123 is formed to have a curved surface with curvatureat an upper end portion or a lower end portion thereof in order to makethe coverage of the insulating layer 123 favorable. For example, in thecase of using positive photosensitive acrylic as a material of theinsulating layer 123, the insulating layer 123 is preferably foamed tohave a curved surface with a curvature radius (0.2 μm to 3 μm) only atan upper end portion. Either a negative type which becomes insoluble inan etchant by light irradiation or a positive type which becomes solublein an etchant by light irradiation can be used as the insulating layer123. Alternatively, the insulating layer 123 can be provided with asingle-layer structure or a stacked structure of an organic materialsuch as epoxy, polyimide, polyimide, polyvinylphenol, orbenzocyclobutene, or a siloxane material such as a siloxane resin.

In addition, plasma treatment can be performed on the insulating layer123 to oxidize or nitride the insulating layer 123; accordingly, asurface of the insulating layer 123 is modified and a dense film can beobtained. By modifying the surface of the insulating layer 123,intensity of the insulating layer 123 can be improved, and physicaldamage such as crack generation at the time of forming an opening or thelike or film reduction at the time of etching can be reduced.

Next, an insulating layer provided on end portions of the substrate 100is removed by etching or the like (see FIG. 2D). Here, at least theinsulating layers 114, 116, and 120 are partly removed, and theinsulating layer 104 is exposed. Note that in the case where a pluralityof panels of light emitting devices is formed from one substrate (in thecase of taking out many panels), an insulating layer is etched in endportions of each region where the panel is formed to be divided intoelements that form the panels.

Next, an element formation layer 124 including the thin film transistors106 and the like is separated from the substrate 100. It is preferableto form a groove by laser irradiation before the element formation layer124 is separated from the substrate 100. Here, the insulating layer 104exposed in the end portions is irradiated with a laser beam, wherebygrooves 128 are formed (see FIG. 2E).

Next, as illustrated in FIG. 3A, an adhesive sheet 130 is attached tothe element formation layer 124. For the adhesive sheet 130, a sheetwhich can be separated by light or heat is used.

The adhesive sheet 130 is attached, whereby stress that is, applied tothe element formation layer 124 can be reduced before and afterseparation and damage of the thin film transistor 106 can be suppressedas well as separation can be easily performed.

Next, the element formation layer 124 is separated from the substrate100 at the interface between the separation layer 102 and the insulatinglayer 104 functioning as a protective layer, by using the grooves 128 astriggers (see FIG. 3B). For example, as a separation method, mechanicalforce (a separation process with a human hand or with a gripper, aseparation process by rotation of a roller, or the like) may be used.

Further, a liquid may be dropped into the grooves 128 to allow theliquid to be infiltrated into the interface between the separation layer102 and the insulating layer 104, which may be followed by theseparation of the element formation layer 124 from the separation layer102. Alternatively, a method can be employed in which a fluoride gassuch as NF₃, BrF₃, or ClF₃ is introduced into the grooves 128, and theseparation layer is removed by etching with the use of the fluoride gasso that the element formation layer 124 is separated from the substratehaving an insulating surface.

In this embodiment, a method is employed in which a metal oxide layer isformed as the separation layer 102 in contact with the insulating layer104, and the element formation layer 124 is separated by a physicalmeans; however, this embodiment is not limited to the method. Forexample, the following method can be employed: a light-transmittingsubstrate is used as the substrate 100, an amorphous silicon layercontaining hydrogen is used as the separation layer 102, the separationlayer 102 is irradiated with a laser beam from the substrate 100, andhydrogen included in the amorphous silicon layer is vaporized so thatseparation is performed between the substrate 100 and the separationlayer 102.

Alternatively, a method by which the substrate 100 is mechanicallypolished and removed, or a method by which the substrate 100 isdissolved and removed using a solution of HF or the like can beemployed. In that case, the separation layer 102 is not required.

Next, on a separation surface (the surface of the insulating layer 104exposed by separation) side of the element formation layer 124separated, the first structure body 132 in which the fibrous body 132 ais impregnated with the organic resin 132 b is provided (see FIG. 3C).Such a structure body is also called a prepreg.

A prepreg is specifically formed in a following manner: after a fibrousbody is impregnated with a varnish in which a matrix resin is dilutedwith an organic solvent, drying is performed so that the organic solventis volatilized and the matrix resin is semi-cured. The thickness of thestructure body is preferably greater than or equal to 10 μm and lessthan or equal to 100 μm, more preferably, greater than or equal to 10 μmand less than or equal to 30 μm. When a structure body with such athickness is used, a thin light emitting device capable of being curvedcan be manufactured.

A thermosetting resin such as an epoxy resin, an unsaturated polyesterresin, a polyimide resin, a bismaleimide-triazine resin, or a cyanateresin can be used for the organic resin 132 b. Alternatively, athermoplastic resin such as a polyphenylene oxide resin, apolyetherimide resin, or a fluorine resin can be used. By using theabove organic resin, the fibrous body can be fixed to the semiconductorintegrated circuit by heat treatment. The higher the glass transitiontemperature of the organic resin 132 b is, the less the organic resin132 b is destroyed by local pressing force, which is preferable.

Highly thermally-conductive filler may be dispersed in the organic resin132 b or the yarn bundle of the fibrous body 132 a. As the highlythermally-conductive filler, aluminum nitride, boron nitride, siliconnitride, alumina, and the like can be given. As the highlythermally-conductive filler, a metal particle such as silver or coppercan also be given. In the case where the highly thermally-conductivefiller is included in the organic resin or the yarn bundles of fibers,heat can be easily released to the outside. Accordingly, thermal storagein the light emitting device can be suppressed and thus the lightemitting device can be prevented from being damaged.

The fibrous body 132 a is a woven or nonwoven fabric using high-strengthfibers of an organic compound or an inorganic compound and a pluralityof fibrous bodies is provided so as to partly overlap with each other. Ahigh-strength fiber is specifically a fiber with a high tensile modulusof elasticity or a fiber with a high Young's modulus. As typicalexamples of a high-strength fiber, a polyvinyl alcohol fiber, apolyester fiber, a polyamide fiber, a polyethylene fiber, an aramidfiber, a polyparaphenylene benzobisoxazole fiber, a glass fiber, acarbon fiber, and the like can be given. As a glass fiber, a glass fiberusing E glass, S glass, D glass, Q glass, or the like can be given. Notethat the fibrous body 132 a may be formed from one kind of theabove-described high-strength fiber. Alternatively, the fibrous body 132a may be formed from plural kinds of the above-described high-strengthfibers or may be fainted from plural kinds of high-strength fibers. Inaddition, a fibrous body is not provided above and below the elementportion 170 including a light emitting element but may be provided onone side of the element portion 170. Note that it is preferable to use amaterial having the same level or substantially the same level ofrefractive index for the fibrous body 132 a and the organic resin 132 b.

The fibrous body 132 a may be a woven fabric which is woven usingbundles of fibers (single yarns) (hereinafter, the bundles of fibers arereferred to as yarn bundles) for warp yarns and weft yarns, or anonwoven fabric obtained by stacking yarn bundles of plural kinds offibers in a random manner or in one direction. In the case of a wovenfabric, a plain-woven fabric, a twilled fabric, a satin-woven fabric, orthe like can be used as appropriate.

The yarn bundle may have a circular shape or an elliptical shape incross section. As the yarn bundle of fibers, a yarn bundle of fibers maybe used which has been subjected to fiber opening with a high-pressurewater stream, high-frequency vibration using liquid as a medium,continuous ultrasonic vibration, pressing with a roller, or the like. Ayarn bundle of fibers which is subjected to fabric opening has a largewidth, has a smaller number of single yarns in the thickness direction,and has an elliptical shape or a flat shape in its cross section.Further, by using a loosely twisted yarn as the yarn bundle of fibers,the yarn bundle is easily flattened and has an elliptical shape or aflat shape in cross section. Using a yarn bundle having an ellipticalshape or a flat shape in cross section in this manner can reduce thethickness of the fibrous body 132 a. Accordingly, the thickness of thestructure body can be reduced and thus a thin light emitting device canbe manufactured.

Next, the first structure body 132 is heated and subjected to pressurebonding so that the organic resin 132 b of the first structure body 132is plasticized, semi-cured, or cured. In the case where the organicresin 132 b is an organic plastic resin, the organic resin which isplasticized is then cured by cooling to room temperature. By heating andpressure bonding, the organic resin 132 b is uniformly spread over thesurface of the element formation layer 124 and cured. A step of pressurebonding of the first structure body 132 is performed under anatmospheric pressure or low pressure.

After pressure bonding of the first structure body 132, the adhesivesheet 130 is removed and the first electrode 122 is exposed (see FIG.4A).

Next, the EL layer 134 is formed over the first electrode 122. The ELlayer 134 can be formed using either a low molecular material or a highmolecular material. Note that, a material forming the EL layer 134 isnot limited to a material containing only an organic compound material,and it may partially contain an inorganic compound material.Alternatively, the EL layer 134 may have at least a light emittinglayer, and a single-layer structure that is formed using a single lightemitting layer or a stacked structure including layers having differentfunctions may be used. For example, functional layers such as a holeinjecting layer, a hole transporting layer, a carrier-blocking layer, anelectron transporting layer, electron injecting layer, and the like canbe combined as appropriate in addition to a light emitting layer. Notethat a layer having two or more functions of the respective functions ofthe layers may be included.

In addition, the EL layer 134 can be formed by either a wet process or adry process, such as an evaporation method, an inkjet method, a spincoating method, a dip coating method, or a nozzle printing method.

Next, the second electrode 136 is formed over the EL layer 134.Accordingly, the light emitting element 140 in which the first electrode122, the EL layer 134, and the second electrode 136 are stacked can beformed. Note that one of the first electrode 122 and the secondelectrode 136 is used as an anode, and the other is used as a cathode.

In the case of being used as the anode, a material with a high workfunction is preferably used. For example, a single-layer film such as anindium tin oxide film, an indium tin oxide film containing silicon, alight-transmitting conductive film formed by a sputtering method using atarget in which indium oxide is mixed with zinc oxide (ZnO) of 2 wt % to20 wt %, a zinc oxide (ZnO) film, a titanium nitride film, a chromiumfilm, a tungsten film, a Zn film, or a Pt film; a stack of a titaniumnitride film and a film containing aluminum as its main component; athree-layer structure of a titanium nitride film, a film containingaluminum as its main component, and another titanium nitride film; orthe like.

A material having a low work function (Al, Ag, Li, Ca, or an alloythereof such as MgAg, MgIn, AlLi, CaF₂, or calcium nitride) ispreferably used for a cathode. In the case where an electrode used as acathode is made to transmit light, a stack of a metal thin film with asmall thickness and a light-transmitting conductive film (an indium tinoxide film, an indium tin oxide film containing silicon, alight-transmitting conductive film formed by a sputtering method using atarget in which indium oxide is mixed with zinc oxide (ZnO) of 2 wt % to20 wt %, a zinc oxide (ZnO) film, or the like) is preferably used as theelectrode.

In this embodiment, the first electrode 122 is used as an anode, and theEL layer 134 has a structure in which a hole injecting layer, a holetransporting layer, a light emitting layer, an electron injecting layerare sequentially stacked from the first electrode 122 side. Variouskinds of materials can be used for the light emitting layer. Forexample, a fluorescent compound which exhibits fluorescence or aphosphorescent compound which exhibits phosphorescence can be used.

Next, the insulating layer 138 is formed over the second electrode 136so as to cover the light emitting element 140. Therefore, the elementportion 170 can be formed. The insulating layer 138 functions as aprotective layer and is provided as a heat insulating layer to preventmoisture or damage from entering the EL layer 134 in the later pressurebonding process of the second structure body or to reduce heating of theEL layer 134 in the later pressure bonding process of the secondstructure body. For example, the insulating layer 138 is formed using aninorganic compound to be a single layer or a multilayer by a sputteringmethod, a plasma CVD method, a coating method, a printing method, or thelike. As a typical example of an inorganic compound, carbon, siliconoxide, silicon nitride, silicon oxynitride, silicon nitride oxide, andthe like can be given. In addition, it is preferable that a film withfavorable coverage be used for the insulating layer 138. Alternatively,a stacked-layer film of an organic compound and an inorganic compoundmay be used for the insulating layer 138. When silicon nitride, siliconnitride oxide, silicon oxynitride, or the like is used for theinsulating layer 138, entry of moisture or gas such as oxygen fromoutside into the element layer to be formed later can be prevented. Thethickness of the insulating layer functioning as a protective layer ispreferably greater than or equal to 10 nm and less than or equal to 1000nm, more preferably, greater than or equal to 100 nm and less than orequal to 700 nm (see FIG. 4B).

Next, the second structure body 133 is provided over the insulatinglayer 138. Similarly to the first structure body 132, a structure bodyin which a fibrous body is impregnated with an organic resin is used forthe second structure body 133. Then, the second structure body 133 isheated and subjected to pressure bonding so that the second structurebody 133 is bonded to the first structure body 132, and the elementportion 170 including the light emitting element 140 is sealed by thefirst structure body 132 and the second structure body 133 (see FIG.4C).

Through the above steps, a light emitting device of this embodimenthaving a light emitting element sealed by the first structure body andthe second structure body can be formed.

As for the light emitting device of this embodiment, the element portion170 is arranged in a substantially central portion in a cross section ofthe light emitting device, and the first structure body 132 and thesecond structure body 133 are in contact with each other and fixed toeach other in the end portions where there is no element portion 170, sothat the element portion 170 is sealed. In addition, the first structurebody 132 and the second structure body 133 include a region where thefirst structure body 132 and the second structure body 133 adhere toeach other so as to surround the periphery of the element portion 170.The first structure body 132 and the second structure body 133 areformed using the same material, whereby adhesion of the first structurebody and the second structure body can be improved.

In the light emitting device of this embodiment, a pair of structurebodies which seals the element portion 170 can function as an impactresistant layer against force (also referred to as external stress)externally given to the light emitting device.

By providing a pair of structure bodies on outer sides of the lightemitting element, force locally applied to the light emitting elementcan be alleviated; therefore, damage, defective characteristics, and thelike of the light emitting device due to external stress can beprevented. Accordingly, a highly reliable light emitting device that isreduced in thickness and size and has tolerance can be provided.Further, a light emitting device can be manufactured with a high yieldby preventing defects of a shape and characteristics due to externalstress in a manufacture process.

This embodiment can be freely combined with any of other embodiments.

(Embodiment 3)

In this embodiment, an example of a method for manufacturing a lightemitting device different from that of the aforementioned embodimentwill be described with reference to drawings. Note that in thisembodiment, a manufacturing process of the light emitting deviceillustrated in FIG. 1A is described as an example.

First, the separation layer 102 is formed over one surface of thesubstrate 100, and the insulating layer 104 is successively formed.Then, a first electrode 150 is formed over the insulating layer 104 (seeFIG. 5A).

Note that the first electrode 150 is an electrode that is used as ananode or a cathode of a light emitting element In the case of being usedas the anode, a material having a high work function is preferably used.For example, a single-layer film such as an indium tin oxide film, anindium tin oxide film containing silicon, a light-transmittingconductive film formed by a sputtering method using a target in whichindium oxide is mixed with zinc oxide (ZnO) of 2 wt % to 20 wt %, a zincoxide (ZnO) film, a titanium nitride film, a chromium film, a tungstenfilm, a Zn film, or a Pt film; a stack of a titanium nitride film and afilm containing aluminum as its main component; a three-layer structureof a titanium nitride film, a film containing aluminum as its maincomponent, and another titanium nitride film; or the like.

A material having a low work function (Al, Ag, Li, Ca, or an alloythereof such as MgAg, MgIn, AlLi, CaF₂, or calcium nitride) ispreferably used for a cathode. In the case where an electrode used as acathode is made to transmit light, a stack of a metal thin film with asmall thickness and a light-transmitting conductive film (an indium tinoxide film, an indium tin oxide film containing silicon, alight-transmitting conductive film formed by a sputtering method using atarget in which indium oxide is mixed with zinc oxide (ZnO) of 2 wt % to20 wt %, a zinc oxide (ZnO) film, or the like) is preferably used as theelectrode.

Next, an insulating layer 152 is formed over the first electrode 150,and the thin film transistor 106 is formed over the insulating layer152. In addition, the insulating layers 114 and 116 are formed over thethin film transistor 106, and the wiring 118 which can function as asource electrode or a drain electrode is formed over the insulatinglayer 116 (see FIG. 5B).

For the thin film transistor 106, various structures such as asingle-drain structure, an LDD (lightly doped drain) structure, and agate overlap drain structure can be used. Here, a thin film transistorhaving a single-drain structure is described.

In addition, the wiring 118 and the first electrode 150 are electricallyconnected to each other. Here, the wiring 118 and the first electrode150 are electrically connected to each other through a conductive layer154. The conductive layer 154 can be formed at the same time asformation of a gate electrode 153 of the thin film transistor 106 (inthe same process).

Next, the insulating layer provided on the end portions of the substrate100 is removed by etching or the like, and then an insulating layer 156is formed so as to cover the wiring 118 (see FIG. 5C). Here, theinsulating layer 152 or the like is removed so as not to expose at leastthe insulating layer 104. Note that in the case where a plurality ofpanels of light emitting devices is formed from one substrate (in thecase of taking out many panels), an insulating layer is etched in endportions of each region that forms the panel, and elements that form thepanels are separated from each other.

Next, the element formation layer 124 including the thin film transistor106 and the like is separated from the substrate 100. It is preferablethat, before the element formation layer 124 is separated from thesubstrate 100, laser irradiation be performed to form grooves. Here, thegrooves 128 are formed by irradiating the insulating layers 156 and 104with a laser beam in the end portions (see FIG. 5D).

Next, a separate film 158 is provided so as to cover at least thegrooves 128 (see FIG. 6A). There is a PET film provided with a siliconeresin as an example of the separate film.

Next, the first structure body 132 in which the fibrous body 132 a isimpregnated with the organic resin 132 b is provided on the surface ofthe insulating layer 156 (see FIG. 6B). Successively, the firststructure body 132 is heated and subjected to pressure bonding, and theorganic resin 132 b of the first structure body 132 is plasticized,semi-cured, or cured.

The first structure body 132 is attached to the insulating layer 156,whereby separation can be performed easily, stress applied to theelement formation layer 124 before and after separation can be reduced,and damage of the thin film transistor 106 can be suppressed.

The separate film 158 is provided before the first structure body 132 isattached, whereby separation failure due to the entry of the organicresin 132 b into the grooves 128 and bonding to the separation layer 102can be suppressed.

Next, the element formation layer 124 is separated from the substrate100 at the interface between the separation layer 102 and the insulatinglayer 104 functioning as a protective layer, by using the grooves 128 astriggers (see FIG. 6C). In addition, it is preferable that the separatefilm 158 be removed after separation.

Next, an insulating layer 159 which is formed such a way that theinsulating layer 104 is etched is formed so as to cover end portions ofthe first electrode 150 (see FIG. 7A). The insulating layer 159functions as a bank (a partition) of the light emitting element. Sincethe first electrode is embedded in the insulating layer 152, the surfaceof the insulating layer 104 does not have a step due to unevenness of awiring. Therefore, the insulating layer 159 functioning as a bank isformed using the insulating layer 104, whereby the thickness of the bankcan be reduced, which is preferable. This leads to reduction inthickness of the light emitting device.

Note that the formation of the insulating layer 159 functioning as abank of the light emitting element is not limited to the above method.For example, the insulating layer 104 may be removed by dry etching toexpose the first electrode 150, and then an organic resin or the likemay be used, whereby the insulating layer 159 may be formed so as tocover the end portions of the first electrode 150. Alternatively, anorganic resin film may be formed over the insulating layer 104, theorganic resin film and the insulating layer 104 may be etched by aphotolithography process with the use of the same mask to expose thefirst electrode 150.

Next, an EL layer 160 is formed over the first electrode 150. The ELlayer 160 can be formed using either a low molecular material or a highmolecular material. Note that a material forming the EL layer 160 is notlimited to a material containing only an organic compound material, andit may partially contain an inorganic compound material. Alternatively,the EL layer may have at least a light emitting layer, and asingle-layer structure that is formed using a single light emittinglayer or a stacked structure including layers having different functionsmay be used. Note that a layer having two or more functions of therespective functions of the layers may be included.

In addition, the EL layer 160 can be formed by either a wet process or adry process, such as an evaporation method, an inkjet method, a spincoating method, a dip coating method, or a nozzle printing method.

Next, a second electrode 162 is formed over the EL layer 160. Therefore,a light emitting element 240 in which the first electrode 150, the ELlayer 160, and the second electrode 162 are stacked can be formed. Notethat one of the first electrode 150 and the second electrode 162 is usedas an anode, and the other is used as a cathode.

Next, an insulating layer 164 functioning as a protective layer isformed over the second electrode 162 so as to cover the light emittingelement 240 (see FIG. 7B). Therefore, the element portion 170 can beformed.

Next, the second structure body 133 is provided over the insulatinglayer 164. Similarly to the first structure body 132, a structure bodyin which a fibrous body is impregnated with an organic resin is used forthe second structure body 133. Then, the second structure body 133 isheated and subjected to pressure bonding to be plasticized or cured, andthe second structure body 133 is bonded to the first structure body 132in end portions where there is no element portion 170. By this process,the element portion 170 including the light emitting element 240 can besealed by the first structure body 132 and the second structure body 133(see FIG. 7C). A step in which the structure body is subjected topressure bonding is performed under an atmospheric pressure or a reducedpressure.

Through the above process, the light emitting device of this embodimenthaving the light emitting element sealed by the first structure body andthe second structure body can be formed.

As for the light emitting device of this embodiment, the element portion170 is arranged in a substantially central portion in a cross section ofthe light emitting device, and in the end portions where there is noelement portion 170, the first structure body 132 and the secondstructure body 133 are in contact with each other and fixed to eachother, so that the element portion 170 is sealed. In addition, the firststructure body 132 and the second structure body 133 include a regionwhere the first structure body 132 and the second structure body 133adhere to each other so as to surround the periphery of the elementportion 170. The first structure body 132 and the second structure body133 are formed using the same material, whereby adhesion of the firststructure body and the second structure body can be improved.

In the light emitting device of this embodiment, a pair of structurebodies which seals the element portion functions as impact resistantlayers against force (also referred to as external stress) externallygiven to the light emitting device. By providing the structure bodies,force locally applied to the light emitting element can be alleviated;therefore, damage, defective characteristics, and the like of the lightemitting device due to external stress can be prevented. Accordingly, ahighly reliable light emitting device that is reduced in thickness andsize and has tolerance can be provided. Further, a light emitting devicecan be manufactured with a high yield by preventing defects of a shapeand characteristics due to external stress in a manufacture process.

This embodiment can be freely combined with any of other embodiments.

(Embodiment 4)

In this embodiment, a method for manufacturing a pixel portion of alight emitting device having a thin film transistor (a thin filmtransistor using an amorphous semiconductor film, a microcrystalsemiconductor film, or the like; a thin film transistor using an organicsemiconductor film; a thin film transistor using an oxide semiconductor;or the like) formed by a process at relatively low temperature (lowerthan 500° C.) will be described. Here, an EL display device is used asthe light emitting device.

A separation layer 302 is formed on one surface of the substrate 100,and then the insulating layer 104 is formed (see FIG. 8A). Theseparation layer 302 and the insulating layer 104 can be formed insuccession. By forming successively, they are not exposed to the air sothat impurities can be prevented from being contained therein.

Note that in this process, the case where the separation layer 302 isprovided on the entire surface of the substrate 100 is described;however, after the separation layer 302 may be provided on the entiresurface of the substrate 100 if needed, the separation layer 302 may beremoved selectively, whereby the separation layer may be provided onlyon a desired region. In addition, although the separation layer 302 isformed to be in contact with the substrate 100, an insulating layer suchas a silicon oxide film, a silicon oxynitride film, a silicon nitridefilm, or a silicon nitride oxide film may be formed to be in contactwith the substrate 100, if needed, and then the separation layer 302 maybe formed to be in contact with the insulating layer.

The separation layer 302 is fowled in such a manner that a layer havinga thickness of 30 nm to 200 nm, which is made of molybdenum (Mo); analloy material containing molybdenum as its main component; or acompound material containing a molybdenum element as its main component,is formed by a sputtering method, a plasma CVD method, a coating method,a printing method, or the like to be a single layer or a stack of aplurality of layers.

In the case where the separation layer 302 has a single-layer structure,a molybdenum layer or a layer containing a mixture of molybdenum ispreferably formed. Alternatively, a layer containing oxide ofmolybdenum, a layer containing oxynitride of molybdenum, a layercontaining oxide of a mixture of molybdenum, or a layer containingoxynitride of a mixture of molybdenum is formed. Note that the mixtureof molybdenum is typically an alloy material containing molybdenum asits main component or a compound material containing a molybdenumelement as its main component, and there is an alloy of tungsten andmolybdenum as an example. However, an embodiment is not limited to this,and molybdenum may be contained.

When the separation layer 302 has a stacked structure, it is preferableto form a metal layer as a first layer and a metal oxide layer as asecond layer. Typically, a layer containing molybdenum or a mixture ofmolybdenum is formed as the metal layer of the first layer; a layercontaining oxide, nitride, oxynitride, or nitride oxide of molybdenum ora layer containing oxide, nitride, oxynitride, or nitride oxide of amixture of molybdenum is formed as the second layer.

When the separation layer 302 has a stacked structure in which a metallayer is formed as the first layer and a metal oxide layer is formed asthe second layer, the stacked structure may be formed as follows: alayer containing molybdenum is formed as the metal layer, and aninsulating layer made of oxide is formed thereover, whereby a layercontaining oxide of molybdenum is formed as the metal oxide layer at theinterface between the layer containing molybdenum and the insulatinglayer. Moreover, the metal oxide layer may be formed in such a mannerthat the surface of the metal layer is subjected to thermal oxidationtreatment, oxygen plasma treatment, treatment using a solution havingstrong oxidizability such as ozone water, or the like.

Note that the substrate 100 and the insulating layer 104 described inEmbodiment 2 can be used as appropriate for the substrate 100 and theinsulating layer 104.

Next, a thin film transistor 304 is formed over the insulating layer 104(see FIG. 8B). In this embodiment, an inverted staggered thin filmtransistor of which channel formation region is formed using anamorphous semiconductor, a microcrystal semiconductor, an organicsemiconductor, or an oxide semiconductor is described as a thin filmtransistor.

The thin film transistor 304 is formed using at least a gate electrode306, a gate insulating layer 308, and a semiconductor layer 310. Inaddition, an impurity semiconductor layer 312 functioning as a sourceregion or a drain region may be formed over the semiconductor layer 310.Further, a wiring 314 that is in contact with the impurity semiconductorlayer 312 is formed.

The gate electrode 306 can be formed to be a single layer or a stackusing not only the metal used for the gate electrode 112 described inthe above embodiment but also a metal material such as chromium, copper,neodymium, or scandium: or an alloy material containing any of these asits main component. Alternatively, a semiconductor layer typified bypolycrystalline silicon doped with an impurity element such asphosphorus, or an AgPdCu alloy may be used. Alternatively, conductiveoxide formed using indium, gallium, aluminum, zinc, tin, or the like orcomposite oxide may be used. For example, indium tin oxide (ITO) may beused for a gate electrode having a light-transmitting property.

The gate electrode 306 can be formed in such a way that a conductivelayer is formed over the insulating layer 104, with the use of thematerial by a sputtering method or a vacuum evaporation method, a maskis formed by a photolithography method, an inkjet method, or the likeover the conductive layer, and the conductive layer is etched using themask.

Alternatively, the gate electrode 306 can be formed by discharging aconductive nanopaste of silver, gold, copper, or the like over thesubstrate by an inkjet method and baking the conductive nanopaste. Notethat to improve adhesion between the gate electrode 306 and theinsulating layer 104, a nitride layer of the metal material may beprovided between the insulating layer 104 and the gate electrode 306.Here, a conductive layer is formed over the insulating layer 104 andetched by a resist mask formed using a photomask.

Note that a side surface of the gate electrode 306 preferably has atapered shape.

This is because disconnection at a step portion is prevented since asemiconductor layer and a wiring are formed over the gate electrode 306in a later process. To form the side surface of the gate electrode 306into a tapered shape, etching may be performed while the resist maskrecedes. For example, an oxygen gas is included in an etching gas,whereby etching can be performed while the resist mask recedes.

In addition, a gate wiring (a scan line) can be formed by the process inwhich the gate electrode 306 is formed at the same time. Note that a“scan line” means a wiring arranged to select a pixel, while a“capacitor wiring” means a wiring which is connected to one electrode ofa capacitor of a pixel. However, this embodiment is not limited to this,and one or both of the gate wiring and the capacitor wiring may beprovided separately from the gate electrode 306.

The gate insulating layer 308 can be formed to be a single layer or astack using silicon oxide, silicon nitride, silicon oxynitride, siliconnitride oxide, hafnium oxide, hafnium aluminum oxide, hafnium siliconoxynitride, or yttria by a CVD method, a sputtering method, a pulsedlaser deposition method (PLD method), or the like. The gate insulatinglayer 308 can be formed using a CVD method, a sputtering method, or thelike. In addition, the gate insulating layer 308 is formed using amicrowave plasma CVD apparatus with high frequency (greater than orequal to 1 GHz), whereby withstand voltage between a gate electrode anda drain electrode or a source electrode can be improved; therefore, ahighly reliable thin film transistor can be obtained.

The semiconductor layer 310 is a layer formed using a non-single-crystalsemiconductor which has a thickness greater than or equal to 10 nm andless than or equal to 200 nm, more preferably, greater than or equal to20 nm and less than or equal to 150 nm. As the semiconductor, silicon,germanium, a silicon germanium compound, and the like can be given. Inthis embodiment, without laser irradiation, heat treatment, and the likebeing performed, the semiconductor layer 310 is formed directly on thegate insulating layer 308 at a low temperature of less than 500° C. Theseparation layer 302 is formed using a layer containing at leastmolybdenum, whereby a separation process can be performed easily evenwhen a thin film transistor is formed at a low temperature of less than500° C.

Note that the semiconductor layer 310 may have a structure in which amicrocrystal semiconductor and an amorphous semiconductor are stackedfrom a side which is in contact with the gate insulating layer.Alternatively, as the semiconductor layer 310, nitrogen or an NH groupmay be provided, and a non-single-crystal semiconductor which includes acrystal grain having an inverted conical shape and/or a micro-crystalgrain having a grain size of greater than or equal to 1 nm and less thanor equal to 10 nm, preferably, greater than or equal to 1 nm and lessthan or equal to 5 nm in an amorphous structure may be used.

Alternatively, as the semiconductor layer 310, an impurity elementimparting one conductivity type such as phosphorus which imparts n-typeconductivity may be added to an amorphous semiconductor or amicrocrystal semiconductor. Further alternatively, as the semiconductorlayer 310, a metal element which forms a silicide by reaction withsilicon, such as titanium, zirconium, hafnium, vanadium, niobium,tantalum, chromium, molybdenum, tungsten, cobalt, nickel, platinum, orthe like may be added to an amorphous semiconductor or a microcrystalsemiconductor. Mobility of a semiconductor layer can be increased byadding an impurity element imparting one conductivity type, a metalelement which forms a silicide by reaction with silicon, or the like;therefore, electron field-effect mobility of a thin film transistor inwhich the semiconductor layer serves as a channel formation region canbe increased.

In addition, the semiconductor layer 310 can be formed using metal oxideor an organic semiconductor material. As typical examples of the metaloxide, zinc oxide, indium gallium zinc oxide, and the like can be given.

The impurity semiconductor layer 312 functioning as a source region anda drain region may be formed in contact with the semiconductor layer310. The impurity semiconductor layer 312 may be formed using asemiconductor layer to which an impurity element imparting oneconductivity type is added. When an n-channel thin film transistor isformed, phosphorus may be used as an impurity element imparting oneconductivity type, and typically, amorphous silicon containingphosphorus or microcrystal silicon containing phosphorus is used. When ap-channel thin film transistor is formed, boron may be used as animpurity element imparting one conductivity type, and typically,amorphous silicon containing boron or microcrystal silicon containingboron is used.

The concentration of an impurity element imparting one conductivitytype, here the concentration of phosphorus or boron is set to 1×10¹⁹ to1×10²¹ cm⁻³, the impurity semiconductor layer to which an impurityelement imparting one conductivity type is added can have an ohmiccontact with the wiring 314, and functions as the source region and thedrain region.

The source and drain regions 312 are formed to have a thickness ofgreater than or equal to 10 nm and less than or equal to 100 nm,preferably, greater than or equal to 30 nm and less than or equal to 50nm. When the source and drain regions 312 are thinned, throughput can beincreased.

The wiring 314 can be formed in a manner similar to the manner in whichthe wiring 118 described in Embodiment 2 is formed. For example,conductive oxide or conductive composite oxide formed using indium,gallium, aluminum, zinc, tin, or the like may be used.

The thin film transistor of this embodiment can be applied to aswitching transistor in a pixel of a light emitting device typified byan EL display device, in a manner similar to the manner in which thethin film transistors described in Embodiment 2 and Embodiment 3 arefowled. Therefore, an insulating layer 316 and an insulating layer 318which cover this thin film transistor are formed (see FIG. 8C).

Next, an opening 321 is formed so as to reach a source electrode and adrain electrode formed by the wiring 314. Note that when the opening 321is formed, the insulating layer 316 and the insulating layer 318 whichare provided in end portions of the substrate 100 are removed by etchingor the like. Here, it is preferable that at least the insulating layer318 be removed and the insulating layer 316 be exposed. Note that in thecase where a plurality of EL panels is formed from one substrate (in thecase of taking out many panels), it is preferable that at least theinsulating layer 318 be etched in end portions of each region that formsthe panel and elements that form the panels be separated from eachother.

Next, a first electrode 322 is provided over the insulating layer 316and the insulating layer 318 so as to be connected through the opening321. Then, an insulating layer 323 is formed so as to cover an endportion of the first electrode 322, in a manner similar to the manner inwhich the insulating layer 123 of Embodiment 2 is formed. In such amanner, the switching thin film transistor in a pixel of the displaydevice which is illustrated in FIG. 8D can be manufactured.

Note that the insulating layer 316 can be formed in a manner similar tothe manner in which the gate insulating layer 308 is formed. Further,the insulating layer 316 is preferably a dense silicon nitride layersuch that entry of a contaminant impurity element such as an organicsubstance, a metal substance, or moisture floating in the atmosphere canbe prevented. The insulating layer 318 can be formed in a manner similarto the manner in which the insulating layer 116 described in Embodiment2 is formed. In addition, the first electrode 322 can be fowled in amanner similar to the manner in which the first electrode 122 describedin Embodiment 2 is formed.

Next, an element formation layer 324 including the thin film transistor304 and the like is separated from the substrate 100. Before the elementformation layer 324 is separated from the substrate 100, it ispreferable that laser irradiation be performed to form grooves 327.Here, the grooves 327 are formed by irradiating the insulating layer 316exposed in end portions, the gate insulating layer 308, and theinsulating layer 104, with a laser beam 326 (see FIG. 8E).

Next, as illustrated in FIG. 9A, an adhesive sheet 328 is attached tothe element formation layer 324. For the adhesive sheet 328, a sheetwhich can be separated by light or heat is applied.

The adhesive sheet 328 is attached, whereby separation in the separationlayer 302 can be performed easily, and stress to be applied to theelement formation layer 324 before and after separation can be reducedand damage of the thin film transistor 304 can be suppressed.

Next, the element formation layer 324 is separated from the substrate100 at the interface between the separation layer 302 and the insulatinglayer 104 functioning as a protective layer, by using the grooves 327 asa trigger (see FIG. 9B). For example, as a separation method, mechanicalforce (a separation process with a human hand or with a gripper, aseparation process by rotation of a roller, or the like) may be applied.

Further, a liquid may be dropped into the grooves 327 to allow theliquid to be infiltrated into the interface between the separation layer302 and the insulating layer 104, which may be followed by theseparation of the element formation layer 324 from the separation layer302. Alternatively, a method can be employed in which a fluoride gassuch as NF₃, BrF₃, or ClF₃ is introduced into the grooves 327, and theseparation layer is removed by etching with the use of the fluoride gasso that the element formation layer 324 is separated from the substratehaving an insulating surface.

In this embodiment, a method is employed in which a metal oxide layer isformed as the separation layer 302 in contact with the insulating layer104, and the element formation layer 324 is separated by a physicalmeans. However, this embodiment is not limited to this method, and thefollowing method can be employed: a light-transmitting substrate is usedas the substrate 100, an amorphous silicon layer containing hydrogen isused as the separation layer 302, the separation layer 302 is irradiatedwith a laser beam from the substrate 100, and hydrogen included in theamorphous silicon layer is vaporized so that separation is performedbetween the substrate 100 and the separation layer 302.

Alternatively, a method by which the substrate 100 is mechanicallypolished and removed, or a method by which the substrate 100 isdissolved and removed using a solution of HF or the like can beemployed. In that case, the separation layer 302 is not required.

Next, a structure body in which a fibrous body is impregnated with anorganic resin is provided on a separation surface of the elementformation layer 324 which is separated (the surface of the insulatinglayer 104 exposed by separation), and then the structure body is heatedand subjected to pressure bonding, whereby the organic resin in thestructure body is plasticized or cured, and the first structure body 132in which the fibrous body 132 a is impregnated with the organic resin132 b is provided on the element formation layer 324 (see FIG. 9C).Fixing of the structure body in which the fibrous body is impregnatedwith the organic resin can be performed under an atmospheric pressure ora reduced pressure. Note that when the organic resin of the structurebody in which the fibrous body is impregnated with the organic resin isa plastic organic resin, the structure body in which the fibrous body isimpregnated with the organic resin is heated and subjected to pressurebonding, and then the organic resin 132 b which is cured by cooling toroom temperature is included.

For the first structure body 132, the first structure body 132 describedin Embodiment 2 can be used as appropriate.

The first structure body 132 is subjected to pressure bonding, and thenthe adhesive sheet 328 is removed and the first electrode 322 is exposed(see FIG. 10A).

Next, an EL layer 360 is formed over the first electrode 322. The ELlayer 360 can be fowled using either a low molecular material or a highmolecular material. Note that a material forming the EL layer 360 is notlimited to a material containing only an organic compound material, andit may partially contain an inorganic compound material. Alternatively,the EL layer may have at least a light emitting layer, and asingle-layer structure that is fowled using a single light emittinglayer or a stacked structure including layers having different functionsmay be used. Note that a layer having two or more functions of therespective functions of the layers may be included.

In addition, the EL layer 360 can be formed by either a wet process or adry process, such as an evaporation method, an inkjet method, a spincoating method, a dip coating method, or a nozzle printing method.

Next, a second electrode 362 is formed over the EL layer 360.Accordingly, a light emitting element 340 in which the first electrode322, the EL layer 360, and the second electrode 362 are stacked can beformed. Note that one of the first electrode 322 and the secondelectrode 362 is used as an anode, and the other is used as a cathode.

Next, an insulating layer 364 functioning as a protective layer isformed over the second electrode 362 so as to cover the light emittingelement 340 (see FIG. 10B). Thus, the element portion 170 can be formed.

Next, the second structure body 133 is provided over the insulatinglayer 364. Similarly to the first structure body 132, a structure bodyin which a fibrous body is impregnated with an organic resin is used forthe second structure body 133. Then, the second structure body 133 isheated and subjected to pressure bonding, and the second structure body133 is bonded to the first structure body 132 in end portions wherethere is no element portion 170, whereby the element portion 170including the light emitting element 340 can be sealed by the firststructure body 132 and the second structure body 133 (see FIG. 10C).

Through the above process, the light emitting device of this embodimenthaving a light emitting element sealed by the first structure body andthe second structure body can be formed.

As for the light emitting device of this embodiment, the element portion170 is arranged in a substantially central portion in a cross section ofthe light emitting device, and in the end portions where there is noelement portion 170, the first structure body 132 and the secondstructure body 133 are in contact with each other and fixed to eachother, so that the element portion 170 is sealed. In addition, the firststructure body 132 and the second structure body 133 include a regionwhere the first structure body 132 and the second structure body 133adhere to each other so as to surround the periphery of the elementportion 170. The first structure body 132 and the second structure body133 are formed using the same material, whereby adhesion of the firststructure body and the second structure body can be improved.

Note that in this embodiment, as a method for forming the elementformation layer 324, the method described in Embodiment 2 is used;however, the method described in Embodiment 3 can be used instead of themethod.

In this embodiment, since a layer containing at least molybdenum is usedfor the separation layer, an element formation layer including a thinfilm transistor to be formed in a process at a low temperature of lessthan 500° C. can be easily separated from the separation layer andcannot be directly formed on a prepreg, and the element formation layeris fixed to the prepreg, whereby an element substrate can be formed. Inaddition, an EL display device can be formed using the elementsubstrate.

(Embodiment 5)

In this embodiment, a method for manufacturing a display device with asmall number of steps will be described. Specifically, a method formanufacturing a pixel portion of a display device having a thin filmtransistor with the use of an oxide semiconductor will be described.Here, an EL display device is used as the display device forillustrative purposes.

The first structure body 132 in which the fibrous body 132 a isimpregnated with the organic resin 132 b is used as a substrate. Notethat the organic resin 132 b with which the fibrous body 132 a in thefirst structure body 132 is impregnated is a cured or semi-cured organicresin.

Before the gate electrode 402 is fowled over the first structure body132 which is a substrate, an insulating layer 400 functioning as a basefilm may be provided between the first structure body 132 and the gateelectrode 402. The insulating layer 400 is a layer which preventsmoisture or impurities such as an alkali metal from diffusing from thefirst structure body 132 to a TFT element and a display device anddeteriorating reliability of a semiconductor element formed on anelement formation layer, and may be provided as appropriate as ablocking layer.

The insulating layer 400 is formed using an insulating material such assilicon oxide, silicon nitride, silicon oxynitride, or silicon nitrideoxide. When the insulating layer 400 has a two-layer structure, forexample, it is preferable to form a silicon nitride oxide layer as afirst insulating layer, and to form a silicon oxynitride layer as asecond insulating layer. Alternatively, a silicon nitride layer may befainted as the first insulating layer, and a silicon oxide layer may beformed as the second insulating layer.

Next, the gate electrode 402 is fowled over the first structure body132, and the gate insulating layer 404 is formed over the gate electrode402 (see FIG. 11A). The gate electrode 402 and the gate insulating layer404 are formed as appropriate using the gate electrode 306 and the gateinsulating layer 308, respectively described in Embodiment 4.

Next, a resist mask formed using a photomask is used, and a contact holeis formed in the gate insulating layer 404, whereby a contact pad of thegate electrode 402 is exposed. At the same time, the peripheral portionof the EL display device may be removed by dry etching.

A semiconductor layer 408 is formed using an oxide semiconductor layer.For the oxide semiconductor layer, composite oxide of an elementselected from indium, gallium, aluminum, zinc, and tin can be used. Forexample, zinc oxide (ZnO), indium oxide. (IZO) containing zinc oxide,and oxide containing indium oxide, gallium oxide, and zinc oxide (IGZO)can be given. An oxide semiconductor can be directly formed on a prepregby using a method in which a film can be deposited at a temperature thatis lower than heat-resistant temperature of the prepreg, such as asputtering method or a pulsed laser deposition method (PLD method).

The semiconductor layer 408 can be fowled by a reactive sputteringmethod or a pulsed laser deposition method (PLD method). Thesemiconductor layer may be formed to have a thickness of greater than orequal to 10 nm and less than or equal to 200 nm, preferably, greaterthan or equal to 20 nm and less than or equal to 150 nm. In addition,when oxygen deficiency in a film is increased, carrier density isincreased, and a property of a thin film transistor is lost. Therefore,oxygen concentration of a film formation atmosphere may be controlled.

In the case of oxide fowled using indium oxide, gallium oxide, and zincoxide, the composition ratio of a metal element has a high degree offreedom, and the oxide formed using indium oxide, gallium oxide, andzinc oxide functions as a semiconductor in a wide range of mixing ratio.A material (IGZO) in which indium oxide (IZO) containing 10 weight % ofzinc oxide and oxide formed using indium oxide, gallium oxide, and zincoxide are mixed at an equimolar ratio can be given as an example.

Here, as an example of a method for forming the semiconductor layer 408,a method using IGZO is described. Indium oxide (In₂O₃), gallium oxide(Ga₂O₃), and zinc oxide (ZnO) are mixed at an equimolar ratio, and atarget with a diameter of 8 inches that is sintered is used with anoutput of 500 W by direct current (DC) sputtering, whereby asemiconductor layer is formed to a thickness of 100 nm under conditionsthat pressure in a chamber is 0.4 Pa and a gas composition ratio ofAr/O₂ is 10/5 sccm. It is preferable that oxygen partial pressure information be set higher than that of formation condition of alight-transmitting conductive film formed using indium tin oxide (ITO)or the like, and it is preferable that oxygen deficiency be suppressed.

After the semiconductor layer is formed, a resist mask which is formedusing a photomask is used, and etching is performed by dilutehydrochloric acid or organic acid, for example, citric acid, whereby thesemiconductor layer 408 is formed (see FIG. 11B). Next, a photoresist isseparated using an organic solvent.

Next, wirings 412 and 414 are formed over the semiconductor layer 408.The wirings 412 and 414 can be formed using a material which is similarto that of the wiring 314 described in Embodiment 4.

After a resist mask is formed over at least the semiconductor layer 408,a conductive layer is formed over the resist mask, the semiconductorlayer 408, and the gate insulating layer 404 by a sputtering method or avacuum evaporation method.

The resist mask is separated, and the wirings 412 and 414 by which partof the semiconductor layer 408 is exposed are formed by a lift-offmethod, as illustrated in FIG. 11C.

Through the above process, a thin film transistor in which asemiconductor layer is formed using an oxide semiconductor can beformed. In a manner similar to the manner in which the thin filmtransistor described in Embodiment 2 is formed, the thin film transistoraccording to this embodiment can also be applied to a switchingtransistor in a pixel of a display device typified by an EL displaydevice.

Next, an insulating layer 418 having openings 420 and 422 is fowled. Theinsulating layer 418 can be formed in a manner similar to the manner inwhich the insulating layer 316 described in Embodiment 4 is formed. Whenthe insulating layer is formed on the entire surface of the substrate, aresist mask is formed by a photolithography method, and the insulatinglayer is etched using the resist mask, whereby the openings 420 and 422can be formed. Alternatively, the insulating layer 418 having theopenings 420 and 422 may be formed by a printing method or a dropletdischarging method.

Next, a first electrode 424 is provided over the insulating layer 418 soas to be connected to the wiring 414 through the opening 420. In such amanner, a switching thin film transistor in a pixel of a display devicewhich is illustrated in FIG. 12A can be manufactured.

Note that the first electrode 322 described in Embodiment 4 can be usedfor the first electrode 424, as appropriate.

By the above process, a thin film transistor can be formed over aprepreg. In this embodiment, a thin film transistor can be directlyformed on the prepreg without .a separation process being used;therefore, the number of manufacturing steps of a flexible elementsubstrate can be reduced.

Next, an insulating film 430 is formed to cover an end portion of thefirst electrode 424 as illustrated in FIG. 12B. The insulating film 430is also referred to as a partition wall, a barrier, a bank, or the like,and a photosensitive or non-photosensitive organic material (polyimide,acrylic, polyimide, polyimide amide, a resist, or benzocyclobutene) oran SOG film (for example, a silicon oxide film containing an alkylgroup) is used with a thickness in a range of 0.8 μm to 1 μm.

Many oxide semiconductors functioning as an active layer of a TFT, forexample, zinc oxide (ZnO), indium oxide (IZO) containing zinc oxide,oxide (IGZO) containing indium oxide, gallium oxide, and zinc oxide, andthe like are n-type semiconductors; therefore, a drain electrode of aTFT in which any of these compounds is included in an active layerserves as a cathode.

On the other hand, when the light emitting element in which an organiccompound serves as a light emitting substance is connected to a TFT anddriven, it is preferable that the light emitting element be connected tothe drain electrode side to avoid a change of gate voltage in accordancewith driving. Therefore, the first electrode 424 that is connected tothe drain electrode serves as a cathode, and an EL layer 431 and asecond electrode 432 functioning as an anode are sequentially stackedthereover (see FIG. 12B). Note that the EL layer 431 can be formed usinga material which is similar to that of the EL layer 134 of Embodiment 2by a dry process such as an evaporation method or a wet process such asinkjet method. In addition, the second electrode 432 is formed by anevaporation method or a sputtering method.

The EL layer 431 is not formed using a single layer and is formed usinga plural-layer structure including an electron injecting layer, anelectron transporting layer, a light emitting layer, a hole transportinglayer, a hole injecting layer, and the like, an electron injectinglayer, an electron transporting layer, a light emitting layer, a holetransporting layer, a hole injecting layer, and the like are stacked inthis order over the first electrode 424 functioning as a cathode, andfinally, the second electrode 432 is formed as an anode. Thus, a lightemitting element 440 in which the first electrode, the EL layer, and thesecond electrode are stacked can be formed.

Note that in order to extract light emitted from the light emittinglayer which includes an organic compound as a light emitting substanceto outside, it is preferable that one or both of the first electrode 424and the second electrode 432 be light-transmitting electrodes made ofindium tin oxide (ITO) or the like or be formed with a thickness ofseveral to several tens of nanometers so as to be able to transmitvisible light.

Next, an insulating layer 433 is provided so as to completely cover thelight emitting element 440. In a manner similar to the manner in whichthe insulating layer 138 is formed, the insulating layer 433 is formedusing an insulating film including a carbon film, a silicon nitridefilm, or a silicon nitride oxide film in a single layer or in a stack inwhich these films are combined. At this time, a film with good coverageis preferably used as the insulating layer 433. Thus, the elementportion 170 having the light emitting element 440 can be formed.

Next, a peripheral portion of the element portion 170 is processed likethe grooves 406 illustrated in FIG. 12B. That is, when there is theinsulating layer 400 functioning as a base film, the insulating layer400, the gate insulating layer 404. and the insulating layer 433 are dryetched to form the grooves 406. The protective film, the insulatinglayer, and the insulating layer 400 functioning as a base film in theperipheral portion of the EL display device are removed, wherebyprepregs can be thermally bonded to each other in a later process. Amixed gas of CHF₃ is used in dry etching; however, this embodiment isnot limited to this.

Next, the second structure body 133 in which a fibrous body 133 a isimpregnated with an organic resin 133 b is provided on the surface ofthe insulating layer 433 (see FIG. 12C). Then, the first structure body132 and the second structure body 133 are heated, and the organic resins132 b and 133 b in the structure bodies are subjected to pressurebonding in the grooves 406 through the opening 422, whereby the organicresins 132 b and 133 b are plasticized or cured to be bonded to eachother.

Through the above process, a light emitting device of an embodiment ofthe present invention having a light emitting element sealed by thefirst structure body and the second structure body can be formed.

As for the light emitting device of this embodiment, the element portion170 is arranged in a substantially central portion in a cross section ofthe light emitting device, and in the end portions where there is noelement portion 170, the first structure body 132 and the secondstructure body 133 are in contact with each other and fixed to eachother, so that the element portion 170 is sealed. In addition, the firststructure body 132 and the second structure body 133 include a regionwhere the first structure body 132 and the second structure body 133adhere to each other so as to surround the periphery of the elementportion 170. The first structure body 132 and the second structure body133 are formed using the same material, whereby adhesion of the firststructure body and the second structure body can be improved.

In the light emitting device of an embodiment of the present invention,a pair of structure bodies which seals an element portion functions asan impact resistant layer against force (also referred to as externalstress) applied to the light emitting device from the outside. Thestructure bodies are provided, whereby force which is locally appliedcan be reduced; therefore, damage or defective characteristics of thelight emitting device due to the external stress can be prevented. Thus,a highly reliable light emitting device that is reduced in thickness andsize and has tolerance can be provided. Further, a light emitting devicecan be manufactured with a high yield by preventing defects of a shapeand characteristics caused by the external stress in a manufactureprocess.

In this embodiment, since a thin film transistor can be formed over theprepreg, the number of manufacturing steps of a flexible elementsubstrate can be reduced. In addition, an EL display device can beformed using the element substrate.

(Embodiment 6)

In this embodiment, another example of a light emitting device forproviding high reliability by using an embodiment of the presentinvention and a method for manufacturing the light emitting device willbe described. More specifically, a method for manufacturing a lightemitting device of an embodiment of the present invention having a pairof impact relief layers on outer sides of (on a side which is a sideopposing a light emitting element) the pair of structure bodiesillustrated in FIG. 1B will be described.

A method for manufacturing a light emitting device of this embodiment isdescribed with reference to FIGS. 13A to 13C. First, the elementformation layer 124 is fowled over the substrate 100, and the elementformation layer 124 is separated from the substrate 100 by using anadhesive sheet in a manner similar to the process described withreference to FIGS. 2A to 2E, FIGS. 3A to 3C, and FIGS. 4A and 4B inEmbodiment 2.

Next, the first structure body 132 and the first impact relief layer 103are stacked, and the first structure body 132 is heated and subjected topressure bonding, whereby the first structure body 132 and the elementformation layer 124 are fixed to each other, and the first structurebody 132 and the first impact relief layer 103 are fixed to each other.A process of bonding the element formation layer 124 to the firststructure body 132, and a process of bonding the first structure body132 to the first impact relief layer 103 may be performed at the sametime, or may be performed separately (see FIG. 13A).

It is preferable to use a material that has a low modulus of elasticityand a high breaking strength for an impact relief layer. For example, afilm having rubber elasticity in which the modulus of elasticity ishigher than or equal to 5 GPa and less than or equal to 12 GPa and themodulus of rupture is higher than or equal to 300 MPa can be used.

Next, the EL layer 134 is formed over the first electrode 122. The ELlayer 134 can be formed using either a low molecular material or a highmolecular material. Note that, a material forming the EL layer 134 isnot limited to a material containing only an organic compound material,and it may partially contain an inorganic compound material.Alternatively, the EL layer may have at least a light emitting layer,and may have a single-layer structure that is formed using a singlelight emitting layer or a stacked structure including layers each havinga different function. Note that a layer having two or more functions ofthe respective functions of the layers may be included.

In addition, the EL layer 134 can be formed by either a wet process or adry process, such as an evaporation method, an inkjet method, a spincoating method, a dip coating method, or a nozzle printing method.

Next, the second electrode 136 is formed on the EL layer 134.Accordingly, the light emitting element 140 in which the first electrode122, the EL layer 134, and the second electrode 136 are stacked can befowled. Note that one of the first electrode 122 and the secondelectrode 136 is used as an anode, and the other is used as a cathode.

Next, the insulating layer 138 functioning as a protective layer isfowled over the second electrode 136 to cover the light emitting element140 (see FIG. 13B). Thus, the element portion 170 can be formed.

Next, the second structure body 133 and the second impact relief layer113 are stacked over the insulating layer 138. A structure body in whicha fibrous body is impregnated with an organic resin is used for thesecond structure body 133, in a manner similar to the first structurebody 132. Then, the second structure body 133 is heated and subjected topressure bonding, so that the second structure body 133 is plasticizedor cured, and the second structure body 133 is fixed to the secondimpact relief layer 113 and the second structure body 133 is bonded tothe first structure body 132 in the end portions where there is noelement portion 170. By this process, the element portion 170 includingthe light emitting element 140 can be sealed by the first structure body132 and the second structure body 133 (see FIG. 13C). A step in whichthe structure body is subjected to pressure bonding is performed underan atmospheric pressure or a reduced pressure.

Accordingly, a light emitting device of an embodiment of the presentinvention which has a pair of impact relief layers and a light emittingelement sealed by a pair of structure bodies can be formed.

Bonding of the first structure body 132 to the first impact relief layer103, and bonding of the second structure body 133 to the second impactrelief layer 113 can be performed by direct-heating and pressuretreatment without a bonding layer because a prepreg that is a structurebody in which a fibrous body is impregnated with an organic resin isused for the first structure body 132 and the second structure body 133.

As illustrated in FIG. 13C, the element portion 170 is placed at acentral portion of the first structure body 132 and the second structurebody 133; in the end portions where there is no element portion 170, thefirst structure body 132 and the second structure body 133 are incontact with each other, and the element portion 170 including the lightemitting element 140 is sealed.

In this manner, with the use of a pair of structure bodies that seals alight emitting element, a highly reliable light emitting device which isreduced in thickness and size and has tolerance can be provided.Further, a light emitting device can be manufactured with a high yieldby preventing defects of a shape and characteristics due to externalstress in a manufacture process.

In addition, if a pair of structure bodies and a pair of impact relieflayers are symmetrically provided with respect to the element portion170 as in this embodiment, force applied to the light emitting devicecan be uniformly diffused, damage of the element portion due to bending,warpage, or the like can be prevented. When a pair of structure bodiesis formed using the same material and has the same thickness and a pairof impact relief layers is formed using the same material and has thesame thickness, this effect can provide an equivalent property;therefore, the diffusion effect of force is further enhanced.

Note that this embodiment can be freely combined with any of otherembodiments.

(Embodiment 7)

In this embodiment, another example of a light emitting device which isdifferent from the light emitting device described in Embodiment 1, anda manufacturing method thereof will be described with reference to FIGS.14A and 14B and FIGS. 15A to 15D.

In this embodiment, an example in which the light emitting deviceillustrated in FIG. 1A in Embodiment 1 is provided with a conductivelayer is described. Since the conductive layer can be provided on theoutermost surface of a light emitting device, a conductive layer may beprovided on each surface of outer sides of a pair of structure bodies(on the side opposing the light emitting element side). Note that in thecase where the impact relief layers are provided on the outer side of astructure body as illustrated in FIG. 1B, conductive layers can beprovided on surfaces of outer sides of the impact relief layer.

The conductive layer diffuses static electricity applied byelectrostatic discharge to discharge it or prevents local electriccharges (localization of electric charges) (prevents local potentialdifference) so that electrostatic breakdown of the element portion 170can be prevented. The conductive layer is formed so as to cover(overlap) both surfaces of the element portion 170 with an insulatorinterposed therebetween. Note that the conductive layer and the elementportion 170 are not electrically connected to each other.

The conductive layer is provided on the entire surface of a regionoverlapped with the element portion 170 so as to cover at least theelement portion 170.

The conductive layer may be provided on each surface of both the firststructure body and the second structure body in the light emittingdevice, or one of the surfaces.

An example in which a conductive layer 180 is provided on an outer sideof the second structure body 133 (on the side opposing the lightemitting element 140 side) is illustrated in FIG. 14A. In addition, anexample in which a first conductive layer 180 a and a second conductivelayer 180 b are provided on an outer side of the first structure body132 and on an outer side of the second structure body 133, respectivelyis illustrated in FIG. 14B. Note that in FIG. 14B, the first conductivelayer 180 a and the second conductive layer 180 b are not electricallyconnected to each other.

When conductive layers are provided on the first structure body 132 sideand the second structure body 133 side, the conductive layers may beformed so as to be electrically connected to each other.

The conductive layers may be formed to cover the entire periphery of alight emitting device (a top surface, a bottom surface, and a sidesurface) (to wrap the light emitting device), or a conductive regionthat electrically connects a pair of conductive layers provided on outersides of both impact resistant layers may be formed. The conductiveregion may be part of a side surface of the light emitting device, ormay be an electrode layer penetrating the inside of the light emittingdevice. Note that the side surface of the light emitting device means asection surface (a divided surface) formed when a plurality of lightemitting elements provided on one insulator is cut (divided) inindividual light emitting elements. The cross section may be entirelycovered by a conductive layer, or may be partly covered.

Note that when a conductive layer is formed so as to cover the entireperiphery of the light emitting device (a top surface (a surface), abottom surface (a back surface), and a side surface), the conductivelayer 180 is formed using a light transmitting material at least for adisplay of the light emitting device or to have a thickness throughwhich light is transmitted.

FIG. 15A is an example in which the conductive layer 180 is formed so asto cover the entire periphery of a light emitting device (a top surface(a surface), a bottom surface (a back surface), and a side surface).FIG. 15B illustrates a structure in which the conductive layer 180covers at least one side surface. FIG. 15C is an example in which thefirst conductive layer 180 a and the second conductive layer 180 bformed on surfaces are electrically connected to each other using anelectrode layer 181 a that penetrates the inside of the light emittingdevice, and FIG. 15D is an example in which the first conductive layer180 a and the second conductive layer 180 b formed on the surfaces areelectrically connected to each other using the electrode layer 181 a andan electrode layer 181 b. A through-hole which forms the electrode layermay be processed by physical treatment such as a needle or a drill, ormay be processed by chemical treatment by etching or the like. Inaddition, a laser beam may be used.

In FIGS. 15A to 15D, since the conductive layers that are electricallyconnected to both the surface and the back surface are provided, a broadregion is protected against static electricity from the outside, and ahigher effect of preventing electrostatic discharge breakdown can beobtained.

After the element portion 170 is sealed by a pair of structure bodies,the conductive layers may be formed by a sputtering method or the likeon the surfaces of the structure bodies. When conductive layers areformed on each of a pair of structure bodies, the conductive layers maybe formed by a plurality of steps.

As illustrated in FIG. 1B, when an impact relief layer is provided on anouter side of a structure body (on the side opposing a light emittingelement), a conductive layer may be formed on the impact relief layerbefore the impact relief layer is bonded to the structure body.

In FIGS. 15A to 15D, at least parts of the first conductive layer 180 aand the second conductive layer 180 b are electrically connected to eachother, and the first conductive layer 180 a and the second conductivelayer 180 b have the same potential.

The first conductive layer 180 a and the second conductive layer 180 bhave the same potential, whereby an effect of protection against staticelectricity can be obtained. Before charge is built up by staticelectricity and an element portion including a light emitting element isdamaged, both top and bottom surfaces in the light emitting device havethe same potential, so that the element portion is protected.

For example, when the first structure body and the second structure bodyeach are a structure body in which a fibrous body is impregnated with anorganic resin, aramid films can be used for the first impact relieflayer and the second impact relief layer, and a titanium film can beused for the conductive layer. When the first structure body and thesecond structure body each have a thickness of greater than or equal to10 μm and less than or equal to 30 μm, the first impact relief layer andthe second impact relief layer each have a thickness of greater than orequal to 3 μm and less than or equal to 15 μm, and the element portionincluding the light emitting element has a thickness of greater than orequal to 1 μm and less than or equal to 5 μm, each thickness of thefirst structure body, the second structure body, the first impact relieflayer, and the second impact relief layer is larger than the thicknessof the element portion; therefore, the element portion can be providedin a substantially central portion, whereby a light emitting devicewhich has high resistance to bending stress can be provided.

The conductive layer may have conductivity, and a conductive layerformed using a conductive material can be used.

For the conductive layer, a film of metal, metal nitride, metal oxide,or the like, or a stack of any of the films can be used.

The conductive layer may be formed using, for example, an element suchas titanium, molybdenum, tungsten, aluminum, copper, silver, gold,nickel, platinum, palladium, iridium, rhodium, tantalum, cadmium, zinc,iron, silicon, germanium, zirconium, or barium; or an alloy material, acompound material, a nitride material, or an oxide material eachcontaining any of the above elements as its main component.

As the nitride material, tantalum nitride, titanium nitride, or the likecan be used.

As the oxide material, indium tin oxide (ITO), indium tin oxidecontaining silicon oxide (ITSO), organoindium, organotin, zinc oxide, orthe like can be used. Alternatively, indium zinc oxide (IZO) containingzinc oxide (ZnO), zinc oxide containing gallium (Ga), tin oxide (SnO₂),indium oxide containing tungsten oxide, indium zinc oxide containingtungsten oxide, indium oxide containing titanium oxide, indium tin oxidecontaining titanium oxide, or the like may be used.

Alternatively, a semiconductor film having conductivity, which isobtained by adding an impurity element or the like to a semiconductor,or the like can be used. For example, a polycrystalline silicon film orthe like doped with an impurity element such as phosphorus can be used.

Still alternatively, a conductive macromolecule (also referred to as aconductive polymer) may be used for the conductive layer. As theconductive polymer, a so-called n-electron conjugated conductive polymercan be used. For example, polyaniline and/or a derivative thereof,polypyrrole and/or a derivative thereof, polythiophene and/or aderivative thereof, and a copolymer of two or more kinds of thosematerials can be given.

The conductive layer can be formed by a dry process such as a sputteringmethod, a plasma CVD method, or an evaporation method, or a wet processsuch as a coating method, a printing method, or a droplet dischargingmethod (inkjet method). Alternatively, various plating methods such aselectroplating or electroless plating may be used.

Note that the conductive layer 180 is fowled using a light transmittingmaterial on at least a display of a light emitting device or is formedto have a thickness through which light passes. When the conductivelayer 180 is provided on another surface which does not serve as thedisplay of the light emitting device, a conductive layer does notnecessarily have a light transmitting property.

Further, a protective layer may be stacked over the conductive layer.For example, it is preferable that a titanium film be formed as theconductive layer and a titanium oxide film be stacked over the titaniumfilm as a protective layer. Even in the case where the conductive layeris provided on a surface of a light emitting device, the conductivelayer can be prevented from being degraded because a protective layer isformed on the outermost surface of the light emitting device.

With the use of the conductive layer covering the element portion 170,electrostatic breakdown (malfunctions of the circuit or damage of asemiconductor element) of the element portion 170 clue to electrostaticdischarge is prevented. Further, with the use of the pair of structurebodies which seals the element portion 170, a highly reliable lightemitting device that is reduced in thickness and size and has tolerancecan be provided. In addition, shape defects and defectivecharacteristics due to external stress or electrostatic discharge canalso be prevented in the manufacturing process, so that a light emittingdevice can be manufactured with a high yield.

(Embodiment 8)

In this embodiment, an example of a method for manufacturing a lightemitting device having a conductive layer that is electrically connectedto both surfaces (a top surface and a bottom surface) of the lightemitting device described in Embodiment 7 will be described withreference to FIGS. 16-A1, 16-A2, 16-B1, and 16-B2. FIGS. 16-A2 and 16-B2are plan views, and FIGS. 16-Al and 16-B1 are cross-sectional viewstaken along lines E-F of FIGS. 16-A2 and 16-B2, respectively.

A light emitting device of this embodiment in a manufacturing process isillustrated in FIGS. 16-Al and 16-A2. A plurality of element portions170 is sealed by the first impact relief layer 103, the second impactrelief layer 113, the first structure body 132, and the second structurebody 133, and a stack 144 is formed. The stack 144 is in a state beforeseparation into individual light emitting devices and includes aplurality of element portions 170. The first structure body 132 and thesecond structure body 133 are in contact with each other in the spacebetween the plurality of element portions 170, a seal region whereadhesion is performed is provided, and the element portions 170 aresealed individually.

The first conductive layer 180 a is formed on the outer surface of thefirst impact relief layer 103, which is the outermost surface of thestack 144, and the second conductive layer 180 b is formed on the outersurface of the second impact relief layer 113.

The stack 144 provided with the first conductive layer 180 a and thesecond conductive layer 180 b is divided into individual light emittingdevices 145 a, 145 b, 145 c, 145 d, 145 e, and 145 f having elementportions (see FIGS. 16-B1 and 16-B2). The light emitting devices 145 a,145 b, 145 c, 145 d, 145 e, and 145 f each include a stack 143 that isformed such that the stack 144 is divided.

In this embodiment, the first conductive layer 180 a and the secondconductive layer 180 b are electrically connected to each other by adivision process of the light emitting device (a division process ofindividual light emitting elements). For a division means, it ispreferable to use a means by which the first impact relief layer 103,the second impact relief layer 113, the first structure body 132, andthe second structure body 133 are melted at the time of division (it ismore preferable to use a means by which the first conductive layer 180 aand the second conductive layer 180 b are melted). In this embodiment,division is performed by laser irradiation.

Conditions such as a wavelength and intensity of a laser beam, and abeam size to be used in the division process are not particularlylimited as far as at least the light emitting device can be divided. Foran oscillator of a laser beam, the following can be used: a continuouswave laser such as an Ar laser, a Kr laser, a CO₂ laser, a YAG laser, aYVO₄ laser, a YLF laser, a YAlO₃ laser, a GdVO₄ laser, a Y₂O₃ laser, aruby laser, an alexandrite laser, a Ti:sapphire laser, or a heliumcadmium laser; or a pulsed laser such as an Ar laser, a Kr laser, anexcimer (ArF, KrF, XeCl) laser, a CO₂ laser, a YAG laser, a YVO₄ laser,a YLF laser, a YAlO₃ laser, a GdVO₄ laser, a Y₂O₃ laser, a ruby laser,an alexandrite laser, a Ti:sapphire laser, a copper vapor laser, or agold vapor laser.

As described in this embodiment, the light emitting devices are dividedinto the individual light emitting devices 145 a, 145 b, 145 c, 145 d,145 e, and 145 f by laser irradiation, whereby resistance value betweenthe first conductive layer 180 a and the second conductive layer 180 bdecreases and the first conductive layer 180 a and the second conductivelayer 180 b are brought into a conductive state. Therefore, a step ofdivision into individual light emitting devices and a step of making thefirst conductive layer 180 a and the second conductive layer 180 bconductive can be performed at one time.

Through the above process, the light emitting devices 145 a, 145 b, 145c, 145 d, 145 e, and 145 f each having a light emitting element can beformed as a light emitting device of this embodiment.

In this embodiment, with the use of the conductive layer covering theelement portion, electrostatic breakdown (malfunctions of the circuit ordamage of a semiconductor element) of the element portion 170 due toelectrostatic discharge is prevented. Further, with the use of the pairof structure bodies and the pair of impact relief layers by which theelement portion 170 is sealed, a highly reliable light emitting devicethat is reduced in thickness and size and has tolerance can be provided.In addition, shape defects and defective characteristics due to externalstress or electrostatic discharge can also be prevented in themanufacturing process, so that a light emitting device can bemanufactured with a high yield.

(Embodiment 9)

In this embodiment, another example of a light emitting device and amethod for manufacturing the light emitting device will be describedwith reference to FIGS. 17A to 17C.

A method for manufacturing the light emitting device of this embodimentwill be described with reference to FIGS. 17A to 17C. First, the elementformation layer 124 is formed over the substrate 100 by a processsimilar to the process illustrated in

FIGS. 2A to 2E, FIGS. 3A to 3C, and FIG. 4A described in Embodiment 2,and the element formation layer 124 is separated from the substrate 100by using an adhesive sheet, and then the element formation layer 124 andthe first structure body 132 are fixed to each other. The firststructure body 132 is plasticized, semi-cured, or cured, and then theadhesive sheet is removed (see FIG. 17A).

Next, the EL layer 134 is formed over the first electrode 122. The ELlayer 134 can be formed using either a low molecular material or a highmolecular material. Note that the material forming the EL layer 134 isnot limited to a material containing only an organic compound material,and may partially contain an inorganic compound material. Alternatively,the EL layer may have at least a light emitting layer, and may have asingle-layer structure that is formed using a single light emittinglayer or a stacked structure including layers each having a differentfunction. Note that a layer having two or more functions of therespective functions of the layers may be included.

In addition, the EL layer 134 can be formed by either a wet process or adry process, such as an evaporation method, an inkjet method, a spincoating method, a dip coating method, or a nozzle printing method.

Next, the second electrode 136 is formed over the EL layer 134.Accordingly, the light emitting element 140 in which the first electrode122, the EL layer 134, and the second electrode 136 are stacked can beformed. Note that one of the first electrode 122 and the secondelectrode 136 is used as an anode, and the other is used as a cathode.

Next, the insulating layer 138 functioning as a protective layer isformed over the second electrode 136 (see FIG. 17B). Accordingly, theelement portion 170 is formed.

Next, grooves 250 are formed in end portions of the first structure body132 where there is no element portion 170 by laser irradiation or thelike. It is preferable that a pair of grooves 250 be formed to sandwichthe element portion 170, more preferably, to surround the periphery ofthe element portion 170. In this embodiment, grooves each having a widthof 100 μm and a depth of 10 μm to 20 μm are formed by laser irradiation.Note that the grooves 250 may be formed before the EL layer 134 isformed.

Next, the second structure body 133 is provided over the insulatinglayer 138. A structure body in which a fibrous body is impregnated withan organic resin is used for the second structure body 133, in a mannersimilar to the first structure body 132. Then, the second structure body133 is heated and subjected to pressure bonding, so that the secondstructure body 133 is plasticized or cured, and bonded to the firststructure body 132 in the end portions where there is no element portion170. The second structure body 133 is subjected to pressure bonding,whereby the second structure body 133 gets into the grooves 250 and thefirst structure body 132 and the second structure body 133 arephysically fixed to each other in the grooves 250; therefore, adhesivestrength can be enhanced. By this process, the element portion 170including the light emitting element 140 can be sealed by the firststructure body 132 and the second structure body 133 (see FIG. 17C). Astep in which the structure body is subjected to pressure bonding isperformed under an atmospheric pressure or a reduced pressure.

Accordingly, a light emitting device of this embodiment having a lightemitting element sealed by the first structure body and the secondstructure body can be formed.

As illustrated in FIG. 17C, the element portion 170 is arranged in asubstantially central portion in a cross section of the light emittingdevice, and in the end portions where there is no element portion 170,the first structure body 132 and the second structure body 133 are incontact with each other and fixed to each other, so that the elementportion 170 is sealed.

In this manner, with the use of a pair of structure bodies that seals alight emitting element, a highly reliable light emitting device which isreduced in thickness and size and has tolerance can be provided.Further, a light emitting device can be manufactured with a high yieldby preventing defects of a shape and characteristics due to externalstress in a manufacture process.

As described in this embodiment, the grooves are formed in the firststructure body 132, and the first structure body 132 is bonded to thesecond structure body 133, whereby adhesive strength between the firststructure body 132 and the second structure body 133 can be improved andfilm separation can be prevented.

This embodiment can be freely combined with any of other embodiments.

(Embodiment 10)

In this embodiment, a modular light emitting device to which an FPC isconnected will be described with reference to FIGS. 18A and 18B. FIG.18A is a top view illustrating the light emitting device formed by themanufacturing method described in the above embodiment. In addition,FIG. 18B is a cross-sectional view taken along a line a-b of FIG. 18A.

The light emitting device illustrated in FIGS. 18A and 18B is formed bya method described in any of the above embodiments and includes aterminal portion 502 and the element portion 170 that is sealed by thefirst structure body 132 in which a fibrous body is impregnated with anorganic resin and the second structure body 133 in which a fibrous bodyis impregnated with an organic resin. The element portion includes alight emitting element, a driver circuit used to drive the lightemitting element, and a switching element used to supply potential tothe light emitting element. The terminal portion 502 includes a wiring504. The wiring 504 can be formed at the same time as a wiring includedin the switching element in the element portion. Further, the terminalportion 502 is sealed by the first structure body and the secondstructure body at the same time as the element portion 170.

The wiring 504 provided in the terminal portion 502 receives a videosignal, a clock signal, a start signal, a reset signal, or the like froma flexible printed circuit (FPC) 505 which serves as an external inputterminal. Note that a structure in which a print circuit board (PWB) isattached to the FPC 505 illustrated in FIGS. 18A and 18B may be used.The light emitting device according to this specification includes notonly a light emitting device body but also a state in which an FPC or aPWB is attached thereto.

In FIG. 18B, a through wiring 503 is formed in a position where thethrough wiring 503 is electrically connected to the wiring 504 providedin the terminal portion 502. The through-hole is formed in the firststructure body 132 and the second structure body 133 by a laser, adrill, a punching needle, or the like, and a conductive resin isprovided in the through-hole by screen-printing or an inkjet method,whereby the through wiring 503 can be formed. An organic resin in whicha conductive particle having a grain size of several tens of micrometersor less is dissolved or dispersed is used for the conductive resin.

For the conductive particle, a conductive paste containing any of metalelements of copper (Cu), silver (Ag), nickel (Ni), gold (Au), platinum(Pt), palladium (Pd), tantalum (Ta), molybdenum (Mo), or titanium (Ti)can be used, for example. In addition, as an organic region contained inthe conductive resin, one or more of organic resins functioning as abinder, a solvent, a dispersing agent, and a coating material for themetal particle can be used. Typically, an organic resin such as an epoxyresin, a phenolic resin, or a silicone resin can be used.

Alternatively, the through wiring 503 may be formed without athrough-hole being formed in the first structure body 132 and the secondstructure body 133. For example, a conductive resin is placed in apredetermined position over the first structure body 132 or the secondstructure body 133; organic resins of the structure bodies are partlydissolved by the reaction of the organic resins included in the firststructure body 132 and the second structure body 133 and an organicresin included in the conductive resin; and metal particles included inthe conductive resin are impregnated with the first structure body 132and the second structure body 133, whereby the through wiring 503 can beformed.

The FPC 505 to serve as an external input terminal is attached to thethrough wiring 503 provided in the first structure body 132 and thesecond structure body 133.

Therefore, the wiring 504 provided in the terminal portion 502 and theFPC 505 are electrically connected to each other by using the conductiveparticles included in the through wiring 503.

Thus, a modular light emitting device to which the FPC 505 is connectedcan be obtained.

This embodiment can be freely combined with any of other embodiments.

(Embodiment 11)

A light emitting device described in the above embodiment can be used asa display portion of an electronic device. An electronic devicedescribed in this embodiment has the light emitting device of the aboveembodiment. By the method for manufacturing a light emitting deviceaccording to the above embodiment, a highly reliable light emittingdevice can be obtained with a high yield. As a result, an electronicdevice can be formed with good throughput and high quality as a finalproduct.

The application range of the light emitting device found using the lightemitting device described in the above embodiment is so wide that thislight emitting device can be applied to electronic devices in allfields. The light emitting device can be used for display portions ofvarious electronic devices such as a display device, a computer, acellular phone, or a camera. The light emitting device described in theabove embodiment is used for a display portion, whereby a thinelectronic device with high reliability can be provided. An electronicdevice provided with the flexible light emitting device described in theabove embodiment such as a display can become a highly reliable productwhich realizes portability and reduction in weight.

The light emitting device described in the above embodiment can also beused as a lighting system. One mode of using the light emitting elementto which the above embodiment is applied as a lighting system will bedescribed with reference to FIG. 19 and FIGS. 20A and 20B.

FIG. 19 illustrates an example of a display device using the lightemitting device to which the above embodiment is applied as a backlight.The display device illustrated in FIG. 19 includes a housing 901, aliquid crystal layer 902, a backlight 903, and a housing 904. The liquidcrystal layer 902 is connected to a driver IC 905. The light emittingdevice described in the above embodiment is used as the backlight 903,and current is supplied through a terminal 906.

By using a light emitting device to which the above embodiment isapplied as a backlight of a display device, a thin backlight with highreliability can be obtained. Accordingly, a thin display device can beprovided. Needless to say, the light emitting device described in theabove embodiment can also be used as a lighting system having a planarshape or a curved surface other than a backlight of a liquid crystaldisplay device.

FIG. 20A illustrates an example in which a light emitting device towhich the above embodiment is applied is used as a desk lamp that is oneof lighting systems.

The desk lamp illustrated in FIG. 20A has a housing 2101 and a lightsource 2102. The light emitting device described in the above embodimentis used as the light source 2102.

FIG. 20B illustrates an example in which a light emitting device towhich the above embodiment is applied is used as an indoor lightingsystem 3001. The light emitting device of an embodiment of the presentinvention can be used as a thin lighting system. Further, this lightemitting device can be flexible.

A lighting system is not limited to those illustrated in FIG. 19 andFIGS. 20A and 20B, and is applicable as a lighting system with variousmodes such as lighting for houses or public facilities. The lightemitting medium of the lighting system of this embodiment is a thinfilm, which increases design freedom. Accordingly, variouselaborately-designed products can be provided to the marketplace.

In this manner, according to the light emitting device described in theabove embodiment, an electronic device with lower power consumption andhigh reliability can be provided. This embodiment can be freely combinedwith any of the above embodiments.

This application is based on Japanese Patent Application serial No.2008-180781 filed with Japan Patent Office on Jul. 10, 2008, the entirecontents of which are hereby incorporated by reference.

What is claimed is:
 1. (canceled)
 2. A light emitting device comprising: an aramid fiber; a first insulating layer over the aramid fiber; a transistor over the first insulating layer; a second insulating layer over the transistor, the second insulating layer comprising a first opening; a wiring over the second insulating layer, the wiring electrically connected to the transistor through the first opening; a third insulating layer over the wiring, the third insulating layer comprising a second opening; a first electrode over the third insulating layer, the first electrode electrically connected to the wiring through the second opening; an EL layer over the first electrode; a second electrode over the EL layer; and a fourth insulating layer over the second electrode, wherein the fourth insulating layer and the second insulating layer are in contact with each other.
 3. The light emitting device according to claim 2, further comprising an aramid fiber over the fourth insulating layer.
 4. The light emitting device according to claim 2, wherein the aramid fiber is impregnated with an organic resin.
 5. The light emitting device according to claim 2, further comprising a first layer, wherein the aramid fiber is positioned over the first layer.
 6. The light emitting device according to claim 5, wherein the first layer is an impact relief layer.
 7. The light emitting device according to claim 2, wherein the first insulating layer and the second insulating layer are in contact with each other.
 8. A light emitting device comprising: an aramid fiber; a first insulating layer over the aramid fiber; a transistor over the first insulating layer; a second insulating layer over the transistor, the second insulating layer comprising a first opening; a wiring over the second insulating layer, the wiring electrically connected to the transistor through the first opening; a third insulating layer comprising nitride of silicon over the wiring, the third insulating layer comprising a second opening; a first electrode over the third insulating layer, the first electrode electrically connected to the wiring through the second opening; an EL layer over the first electrode; a second electrode over the EL layer; and a fourth insulating layer over the second electrode, wherein the fourth insulating layer and the first insulating layer are in contact with each other.
 9. The light emitting device according to claim 8, further comprising an aramid fiber over the fourth insulating layer.
 10. The light emitting device according to claim 8, wherein the aramid fiber is impregnated with an organic resin.
 11. The light emitting device according to claim 8, further comprising a first layer, wherein the aramid fiber is positioned over the first layer.
 12. The light emitting device according to claim 11, wherein the first layer is an impact relief layer.
 13. The light emitting device according to claim 8, wherein the first insulating layer and the second insulating layer are in contact with each other. 